Basement floor replacement under fresh water tank

I would try and find the source of the previous leak to mitigate the risk of it happening again.

I would use treated (yellawood, wolmanized) plywood, probably 5/8" thick.

Why not go with a sheet of aluminum and eliminate the problem forever? For about $300 you can buy a 4 x 8 sheet of 3/16" thick aluminum which, with the metal braces, would be more than strong enough to support the water tank.

Our Phaeton floor rotted due to a cracked basin nut on the shower drain above the tanks. Tiffin has came up with a 1" composite plastic sheet to replace the vinyl clad treated plywood panel used before, this has been the standard for construction for several years now.

I'm a little surprised your Tuscany does not have an insulated subfloor the tanks set on, but use at least 5/8" marine ply, with a 16 gauge galvanized sheet metal cover on the bottom for protection. You can either use contact cement, or construction adhesive to attach it to the ply. If you do not have a fresh water tank drain now, I certainly install one at this time. Don't worry about the size of the tanks, but how much water they will hold. Use 8 pounds per gallon for weight that the floor must carry.

The subfloor did have the metal layer on the bottom and some sort of fiberglass looking stuff on the top but the wood just delaminated badly. All of it is out now. I like the idea of the poly vinyl sheet as the base. Never worked with it. Does anyone have any experience working with this stuff?

I replaced the floor in my coach back in the 2000 or so an then replaced 1/2 of it again maybe in the 2010 time frame. I should have done the whole thing but now I am looking at doing the other 1/2 before the tanks drop out! I used 3/4 marine plywood as that's what the original configuration was. There were drains from the tanks going through the floor but there were no drains for water leaking into the compartment. I think you will find that this is a fairly normal configuration. I am going to have to pull the tanks and put in a new floor in the 1/2 I did not but dang, I really hope to put it off until I see the tanks hanging down from the underside!

Poly vinyl sheet does not have very good structural strength, or sheer resistance. An engineered plastic similar to what thor has used may be a acceptable substitute. It can be worked just like wood, using the same tools. You may need to add more supports to add strength for the plastic substitute.

AikenRacer wrote:
The floor underneath my fresh water tank was rotten. Just demo'd it. Pulled out the water tank. Plan is to clean up the metal support structure, put in a new floor and install the water tank back. The replacement floor will be about 4x8' with a cut out for the dump valves. Couple of concerns..
1) What do I use for the flooring? Need protection from road hazards on bottom and it needs to be strong enough to support a 6' x 4' vinyl water tank (there are 2 metal cross braces). Thinking about a sheet of marine plywood.
2) There was no drain anywhere on the old floor. Should there be one and if so, what kind?
Any comments welcome.
Thanks!

You may want to consider using synthetic decking boards and spread them out a little where necessary for your drain and overflow vent lines. They're strong, won't rot, may be easier to install than one piece material and shouldn't require any drilling for the lines. One bolt or screw at each end should be enough for securing them, so they just might work out for you.
Of course I'm not seeing what you're seeing, so............

Just finished this job. New black HDPE flooring in this compartment. No real problems. HDPE was fairly easy to work with. One single sheet did it. Notched it out for the drop pan under the black and gray valves. I did weld in two additional cross braces. Too bad the factory doesn't use better stuff to begin with...