Fella's;
Not sure to just what is being called a document safe here. If it's data storage, that's one thing, if it's just paper storage, that's another.
A data storage safe is required to hold the interior temperature to 125 degrees f, or less, during the test cycle. The data being referred to in this case are photographic material, magnetic tape, and CD discs. It would be unusual to find this type of safe with an interior large enough to accommodate long guns.
There are safes that do not have a moisture content in the insulation to provide the thermal protection required to meet the U.L. 1 hour fire test standards. These are not necessarily 'document' safes though. They can be had in any practical size to protect larger objects, such as guns.
There are many smaller home type RSC's that do use moisture impregnated insulation to protect the contents, however. You should be sure of what it is you've got & not just assume that because it's a 'document safe' there's no chance of moisture damage to your guns. The caveat being, that if you suck all the moisture out of the insulation, you lower the protective ability of that insulation.
900F