We have a very uneven floor situation and we were wondering if anyone has any ideas on how to fill it and make it more even before insulating and sub-floor? Any suggestions would be greatly appreciated! Thank you!!
Below are some pictures while cleaning the floor and you can see where the water just puddled.
Why don’t you guys try putting a strong metal sheet across it to even it out?
Take a look at 3/4 inch Azek. Cellular PVC Can be used like wood, Waterproof. Fire resistant. Can be glued so it is like one piece. Downside $$$
Hello guys…I just heart from a painting technique which is called fluid painting…I dont know much about it but it could look very nice. this technique I know creates an even surface but it can get quite tricky as you will need a Lot of paint…and have to slowly put it on. So it will be a process of putting it on…letting it dry…put some more on…letting it dry…and so on. Buuut the result can be very impressive 
just an idea:)
Good luck and sweet greets,
Lu 
We had this exact problem in our Ford Transit. We fixed the timber batons to the floor in a grid shape as planned and then used Kingspan insulation boards fitted between the batons as our floor insulation. We fixed 12mm ply on top on this as our floor. There was too much flex in the ply floor when we walked over the areas that had been dented, so we cored some holes in the ply and insulation using a drill in the areas with flex and used a can of expandable foam with a long nozzle to fill the gaps under the ply. It would work to lay your floor batons and insulation and the used expandable foam to fill in the gaps before you lay you floor surface, cutting off any lumps. I hope that makes sense!
I love the idea of expandable foam under a plywood floor. The extra insulation will keep out cold in the winter and also the heat from the differential and exhaust system.
That is what we were thinking about doing but wasn’t sure about the strength and compression of the expandable foam. Have you had any problems overtime with it compressing @Rachelp ? We are thinking about building it up a little more with wood and then filling it in with the expandable foam insulation because it is a rather large dip we have.
I don’t think you would have any problem with it compressing over time.
If you will be traveling in hot or cold areas My impulse is to frame with 2x2’s / fitted 2x4’s and fill with foil faced foam sheets. Place some 2x2 on high point, balance a straight edge across 2x2 front to back.measure every 24 inches from sheet metal to bottom of straight edge. Rip 2x to match, Insulate, cover with plywood.
