Wow - you have OSB (oriented strand board) floors that are in good shape? OSB turns to wet cardboard whenever there is water intrusion, which in an Airstream in the Pacific north west is almost inevitable. If yours is truly in good shape and shows no water damage, I don't know that I'd use Kilz - instead I'd seriously consider some kind of penetrating waterproofing agent - possibly the resin they use in fiberglass fabrication. Around the edges, it would need to be thinned to penetrate under the channel. Be extremely thorough around the toilet and any place where plumbing or wiring
And if you have the belly pan off, do the bottom side too, and make sure whatever insulation you have beneath the pan, will drain moisture, and that there's some way for it to escape the belly pan. I've used a dremel and the tiniest drill bit I could find to put some very small holes in the belly pan. Might get ants, but I can always spray for them.
Do some searching for "Floor Rot" to see what others have done.
Vinyl planks - some are great, others NOT. The ones that click together seem to work well but the flexible ones shrink and expand way too much and can tend to buckle. I WATCH other people do this kind of work - and I've also noted that it's a good idea to make allowances for expansion and shrinkage on any flooring that's not glued down. Most people drill relief holes in the flooring before putting in nails or screws that fix cabinets to the wall, etc. (I chose Marmoleum for my Avion; Really liked the commercial rubberized flooring - which in a non-commercial setting should last 50 years - but the cost - O my goodness gracious me! Marmoleum sheet isn't cheap, and it'll surely outlast me so I "settled".
Re-doing a floor is an expensive pain you don't want to have to repeat more than once in 20 years. So take your time and choose everything carefully.
Here's a good link - you might even want to go back to the beginning: