Please recommend a waterproof paint product for wood

[QIS]

That sounds like a neat project for your enterprise! That is small enough so that you can experiment at a reasonable cost. Obviously marine urethane is going to work fine,but,you can try garage floor paint and truck bed liner coating. I thing both are at the big stores. You are in a VERY arid region so don't seal the side not exposed to moisture. Just give that a nice, breathable treatment like stain or cwf. Do a great job of sealing the other five surfaces with your "paint" or whatever you use.

[TrapperL]

I'd look at Red Guard at Home Depot for the water proofing. I'm not sure about it in a floor environment and you probably want to ask. I'd top coat it with a Urethane floor paint. The Urethane alone is pretty stout stuff in a floor environment but its hardly a water proofing.

[trapperwv1]

If you can find Fabulon floor finish it would work or back to the marine grade spar varnish

[mkarch]

I'll ask - why do you need to replace the flooring? Just because it's moisture damaged over time or is there some other reason?

If you have a cheap enough source for cedar or redwood, you may be able to use rough-sawn planks that will last a decade or more without any treatment, and they're "organic". For instance, I get 2x6x6' boards for $4.20 each. To do an 8x12 floor it would run about $135. If you could design it to use cheaper 5/8" or 1 inch thick dimensional boards meant for fencing, cost would be lower. I've even seen some low end cedar decking for as little as $0.75 a square foot.