Trimming out the basement

I am using corrugated plastic sheets from a sign shop to enclose the under side of the trailer. I have work to do building out the "basement". The four trays visible will hold the batteries for the solar system, forward of that is the area where the recess will be for the stabilizer jacks, and forward of that , closest to the nose, is where the kitchen plumbing will be installed. BTW: here is a link to a free book about how to design and build off grid?RV plumbing systems: www.rvst.org/RVIA_Textbooks/Plumbing_Systems.pdf
I got some sign board, corrugated plastic to install on the under-belly of the trailer.
  the extra material around the jack and the profile of the recess I need to build
cutting away the area to build the jack recess.

  I have built tents, one side of which has a vent in it to channel air to the battery compartment. As seen from the under-side.

Trimming the jack wells in metal, and of course, CAULK! A good girl's gotta love some caulk!Here is the tread plate that will be the final exterior facing of the jack wells.Before the kitchen sink tank and other plumbing can go in, the basement has to be insulated and the support grating installed.