Carpet can certainly hold moisture, but in a gun safe that has a Goldenrod on continuously it is a moot point. I repurposed a 5200 lb. Mosler safe into a gun safe in 2002. Stripped all the cabinetry out and lined it all with short loop carpet, and installed a Goldenrod. It's lived 20 years in an unheated space on a concrete slab and there's never been one even minute issue with rust, or moisture issues of any kind.

May God bless America and those who defend her.