Hook a brother up. I'm having some trouble finding solid info on YT.
but, its about that time. So. Send on some good links please.
TheHossUSMC had a series of videos about it... but he removed them for some reason. He used pvc drain pipes... 6" and 8". He dug a hole with a post-hole digger, put the 8" sleeve in it (open at both ends), then put the 6" cache tube into the sleeve. The 6" tube was capped at the bottom end, and had a threaded collar with a threaded plug at the top end. Be sure to use pvc epoxy/glue on the bottom cap and top collar, but not on the threads... of course. You can make a handle for pulling it out with by using zip ties. Also, before you cover with dirt, cover the the opening with a piece of plastic sheeting to keep too much dirt from falling in between the cache and sleeve (defeating the purpose of the sleeve).
EDIT: Some pistol gripped weapons may not fit into a 6" diameter pipe. In that case, use an 8" pipe for the cache and 10" corrugated pipe for the sleeve.
EDIT2: Also, some silica gel packs would be a good idea (available at amazon).