I have a friend that use to oil up a gun to the point it was dripping. I accused him of dipping them in a 55 gal drum.
I store most of my firearms muzzle up but to make room in the safe I set in a row muzzle up and another row muzzle down either just between or just in front. With 30 & 32" guns to the back and 26"-28" to the front, let's the heel of the stock cradle between the barrels of the rear gun. It doubles the capacity of the safe. Also instead of carpet (which I feel can hold moisture) I line the bottom of the safe with cork. 1/8" -3/16" flooring cork works excellent.
Alternating them to increase the capacity of the safe is a great idea; thanks for posting that. I would like to get a couple more into my safe and that would make it possible to do it.
I have always stored mine muzzle up for a couple of reasons. The main one is to avoid damage to the muzzle of my rifles. I know that it shouldn't happen in a carpeted safe, but stuff happens and I've always been a bit overprotective of my rifles. I cringe when I see folks carrying a nice rifle muzzle down in a truck.
Another reason is I've always been paranoid about the possibility of getting something into the barrel of a shotgun that turns into a barrel obstruction. I check the barrels when loading any break action gun, but I don't with a semi auto.