Ammo Can Cigar Humidor: Build & Season Guide

Building a functional ammo can humidor requires a clean surplus ammunition can, untreated Spanish cedar, a digital hygrometer, and two-way humidity packs.

• A surplus military ammo can. Steel ammunition boxes in .50-cal and .30-cal configurations are the two standard sizes found in surplus shops. The .50-cal can is the larger option, offering enough internal room to hold roughly a couple dozen to several dozen cigars depending on their ring gauge and how you stack them. The .30-cal container is smaller, which suits a compact desktop setup or travel case holding a smaller collection. Inspect the can before purchase to confirm the metal latch closes with firm mechanical tension and the rubber gasket inside the lid remains pliable.
• Spanish cedar lining. Untreated Spanish cedar regulates moisture swings and imparts the classic aroma associated with premium cigar storage. You can purchase a pre-made ammo can humidor insert kit with pre-cut panels that slide straight into a standard metal can, which eliminates precision cuts. If you prefer a budget approach, purchase thin, flat sheets of Spanish cedar (typically 1/8 inch to 1/4 inch thick) and trim them to fit the base and walls by hand.
• A digital hygrometer. Analog dial gauges frequently drift several percentage points away from true readings and fail to reflect sudden moisture shifts. A compact digital sensor gives accurate, real-time readouts of both relative humidity and ambient temperature inside the dark metal box. Browse our picks for cigar hygrometers to find a slim unit that mounts easily against an interior cedar wall.
• Boveda seasoning and maintenance packs. Fresh Spanish cedar absorbs significant moisture, so you must condition the dry wood before adding tobacco. Pick up an 84% Boveda seasoning pack to saturate the cedar lining during initial setup. Once seasoning concludes, swap to maintenance packs holding 65% or 69% relative humidity. For pack sizing, use Size 60 packs (roughly one pack per 25 cigars of capacity) for desktop-scale containers like a .50-cal can, or Size 8 packs (roughly one pack per 5 cigars) for lighter loads in a .30-cal container, as outlined in our Boveda cigar humidity packs guide.
• Hand tools and adhesives (if cutting cedar manually). If you skip a pre-cut insert kit, keep a utility knife, a steel straightedge, fine sandpaper, and odorless wood glue or double-sided tape nearby. Fasten the panels securely against the steel walls without getting adhesive on the exposed face of the cedar.

Converting an ammunition can into a seasoned humidor follows a clear six-step sequence from gasket inspection to the final humidity check.

1. Inspect and clean the surplus can. Open the can and examine the perimeter rubber gasket recessed in the lid to ensure it is flexible, free of dry rot, and securely seated in its channel. Wipe the interior metal surfaces with a damp cloth to lift dust or storage grime, then let the container dry completely in open air. Check for major rust on older surplus cans before proceeding, as flaking rust particles can fall into your cigars and degrade the seal along the rim.
2. Line the interior with Spanish cedar. Fit Spanish cedar panels along the floor and four vertical walls of the box. If you are using a pre-cut ammo can humidor insert kit, slide the interlocking pieces into the metal can until they rest snugly against the walls. If you are fitting raw sheets by hand, measure each interior side, score the thin wood with a utility knife along a metal ruler, and snap the cuts clean. Affix the panels against the metal shell using thin strips of double-sided tape or small dabs of wood glue on the back side of each board.
3. Season the cedar lining with an 84% pack. Place an 84% Boveda seasoning pack inside the lined box and clamp the heavy latch shut. Keep the can closed for 2 to 4 weeks, opening it briefly every few days to monitor the internal reading. Dry cedar pulls moisture rapidly from the air, and this prolonged conditioning period brings the cell structure of the wood into balance so it will not absorb essential oils from your cigars later.
4. Swap to your maintenance humidity packs. Take out the 84% seasoning pack once the conditioning window ends. Replace it immediately with maintenance packs rated at 65% or 69% relative humidity, sized to match your container capacity. Because an ammunition box features a non-porous steel shell and a continuous rubber seal, moisture cannot escape through the walls. A 65% pack provides plenty of humidity for most smokers without risking over-saturation.
5. Load your cigars and digital hygrometer. Place your cigars inside the seasoned box, arranging them flat across the cedar base or stacking them inside cedar divider trays. Position your digital hygrometer facing upward near the top of the stack so you can read the screen the moment you open the lid. Clamp the exterior latch firmly to re-engage the rubber seal.
6. Monitor readings over the first 48 hours. Check your hygrometer once per day over the first two days after adding your cigars. The humidity reading often drops a point or two when you first introduce cigars, then stabilizes as the internal atmosphere reaches balance. Maintain storage conditions around 65 to 70% relative humidity and roughly 70°F (21°C), following the proven 70/70 rule explained in our guide on how to store cigars.

Selecting pre-cut components and monitoring gasket condition will ensure your ammo can humidor maintains steady humidity over years of storage.

• Buy a pre-cut cedar insert kit to skip the carpentry. Custom-cut ammo can humidor insert kits feature pre-notched cedar sections designed specifically for standard surplus containers. If you lack fine woodworking tools or want to complete the build in five minutes, an insert kit removes the measuring and trimming entirely.
• Choose a .50-cal can over a .30-cal model for growing collections. A .30-cal ammunition can fills up quickly once you add a digital hygrometer, a cedar floor, and a Size 60 humidity pack. Opting for the larger .50-cal size gives you the headroom needed to store multiple cigar sizes and rotate your collection comfortably without crowding the lid.
• Test the rubber gasket with a paper strip. Close the lid on a small slip of printer paper so half sits inside and half extends outside the latch edge. If you can pull the paper out with zero resistance while the latch is clamped, the rubber gasket is compressed or brittle and will allow moisture to escape.
• Keep the metal box away from direct heat and sunlight. Steel conducts heat much faster than dense Spanish cedar or hardwood cabinets. Store your ammo can humidor inside an interior closet, pantry, or shaded shelf where household temperatures stay stable. Rapid temperature swings alter relative humidity quickly, as detailed in our cigar humidity guide.
• Air out the container briefly every few weeks. Because a surplus metal ammunition box is completely airtight, fresh air never circulates on its own. Pop the latch for 30 seconds every two to three weeks when selecting a cigar to introduce fresh oxygen and check pack softness.

Most failures with ammunition can humidors trace back to skipping the seasoning cycle, applying chemical finishes, or relying on a damaged rubber gasket.

• Loading cigars into dry, unseasoned cedar. Placing premium cigars into raw, unconditioned Spanish cedar pulls moisture straight out of the tobacco leaves within days. This drying ruins the cigar wrapper, causes uneven burns, and strips away subtle flavors before you ever strike a match.
• Finishing or staining the interior cedar face. Never coat the interior cedar with wood stain, varnish, paint, or polyurethane. Chemical finishes clog the natural pores of Spanish cedar, preventing the wood from buffering humidity while releasing noxious fumes that permanently ruin the flavor of your tobacco.
• Trusting a cracked or dried-out surplus gasket. Surplus ammunition cans often sit in storage yards for decades. Over time, temperature shifts in surplus yards dry out, flatten, or crack natural rubber seals. A damaged gasket turns an airtight container into an ordinary leaky metal box that constantly drains your humidity packs.
• Undersizing the maintenance humidity packs. Using a single tiny packet meant for a pocket travel case inside a full .50-cal ammunition box causes the pack to dry out within weeks. Use a Size 60 pack for desktop-scale containers to maintain steady humidity levels over several months without frequent pack replacements.
• Wiping down raw cedar sheets with a wet sponge. Wiping liquid water across thin cedar panels can cause the delicate wood to warp, buckle, and detach from the metal walls. Excess liquid trapped inside an airtight metal container also creates conditions for mold growth, and warm damp environments can encourage dormant cigar beetles to hatch.

Once your ammo can humidor is assembled and holding a steady reading, log your inventory and maintenance dates in our free Humidor Tracker to monitor when your humidity packs need replacement.