Water damage in the underbelly of my TT

I sort of touched on this topic in another thread that I had created in regards to a leak that I had, under the shower of my TT. I feel like the said thread has now been lost in the shuffle. The leak has since been fixed, but the rear portion of my TT's underbelly has been removed to eliminate some water damage that I found during this process. Before I run out to Home Depot and just pick up any material that I feel would work, I wanted to ask you all for some help. When I say that a portion of the underbelly has been removed, I have removed the chloroplast waterproofing sheet (tarp-like sheet), and a thin balsa-like wood board. The styrofoam insulation is still there because it is still in good shape. My questions are as follows. Thanks in advance and sorry for so many questions. Just want to make sure I do things right.

- What should I be using to replace the wood board with? The board that was in there was thin, but seemed to soak up water like a sponge. I would like to replace it with something a little more water resistant, but still just as light weight and thin.

- It looks like this wood board was secured using an adhesive. Would I just buy a good construction adhesive? Is there one in particular I should use?

- What exactly is the chloroplast waterproofing sheet of plastic? What do I need to replace this with? I've heard that craft stores or sign shops have material that would work for this. I want the best option for waterproofing and a rodent deterrent.

- When securing this plastic sheeting I was going to use staples. Is this sufficient in making sure it doesn't start flapping in the wind while pulling my TT?

- If I'm forgetting anything please let me know.

The board is probably luan plywood, a light weight and inexpensive material. You can use more luan or some other plywood, but I would apply some sort of waterproofing or sealer in case of future leaks. Even just a primer paint would help a lot if there is another leak.
I'm not clear on where this "chloroplast" goes. You are talking about the Coroplast brand corrugated plastic stuff, right?  I've not seen that in an RV, just a vapor barrier membrane under the flooring and a thicker waterproof underbelly membrane as the outside bottom layer. Use the stuff sold for mobile home belly pans for that - it should be sturdy enough.

Here is one source with some products that might help:
http://www.randgsupply.com/Warehouse/Exterior/underbellyclosure.htm

Gary RV_Wizard said:

The board is probably luan plywood, a light weight and inexpensive material. You can use more luan or some other plywood, but I would apply some sort of waterproofing or sealer in case of future leaks. Even just a primer paint would help a lot if there is another leak.
I'm not clear on where this "chloroplast" goes. You are talking about the Coroplast brand corrugated plastic stuff, right?  I've not seen that in an RV, just a vapor barrier membrane under the flooring and a thicker waterproof underbelly membrane as the outside bottom layer. Use the stuff sold for mobile home belly pans for that - it should be sturdy enough.

Here is one source with some products that might help:
http://www.randgsupply.com/Warehouse/Exterior/underbellyclosure.htm

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Thanks as always Gary. I've got her all fixed up and ready for the next trip. Now time to look at resealing the roof. Thanks again!