Waterproofing van floor before WFP install?

[Pjj]

You can paint the ply with it , it’s just not very robust stuff and damages easily 

 

[Iron Giant]

As @Pjj says it will come off, more so with ply as it's like a metal bed liner paint which means for metal, I have a my electric reel mounted on some board which I painted and it has come off in places just with been caught with pole hose get pulled out of the van, alos moisture will find it's way underneath if you don't do a proper job and you need to do a proper job