Both Larry and Lonnie have done this mod as well. It occurred to me as read through the old post I never put up pictures of the finished product.
you can see where I screwed into the cross-member where possible In addition where there was not a member I added a small piece of square aluminum in top of the I-Beam flanges for extra support and screwed into that
around the sewer pipe
Under the water tank
We used 4MM Coroplast and the joints are plastic lattice edge form Lowes We tried some paneling joints but it was to hard to get the coroplast into it. The lattice has worked well so far. If you find something else that connects them better please let everyone know. You can see We still have not cut the entryway to the slide motors or to the dump valves this is simply because We have not needed to get in there they are framed out with square aluminum tube . 1 thing I noticed is Crossroads screwed into the base of the I-Beam but never the web so I avoided this as well. There are several screws in the cross-members so I did not feel that a few more would cause any damage.
Good Luck and Happy Camping
Edited by: mapachoo