Jimmy: Muzzle down on a block of wood can still lead to rust if the wood is unfinished/unsealed, because the wood will always have some residual moisture. Even the most expensive kiln dried hardwoods will still be at 6-8% moisture content (usually) and can absorb moisture from the air when the humidity is higher than that. If you want to rest the muzzles on something that won't promote rust, go to your local restaurant supply and get a polyethylene (or is it polypropylene?) cutting board and make your muzzle rest out of strips of the cutting board. Absolutely no chance of moisture absorption from the air, and minimal chance of condensation forming on the surface of the board because there is not much thermal mass. Plus, the surface is often textured so there is minimal physical contact between the muzzles and the plastic. A silicone-treated gun sleeve is a good idea, after the gun is oiled or waxed for storage.
