This is what I was facing-a 90 inch by 66 inch huge hole in the back of the trailer. I had to call up my uncle, who has construction experience, to do much of the labor on this part. Note the silver beam on the bottom-I'll get to that below.
First I had to install outlets for gray water (left), clean water (center), and a propane hose for the on demand hot water heater. The floor is solid steel and impossible to drill through, so I had to use foil tape to hold it in place until I...
...could get forms in in order to use spray foam to hold it in place. I just cut up a piece of cheap cardboard.
Spray foam was the only way to hold the pipes in place since I couldnn't use brackets.
This baseboard is a piece of redwood which my uncle sheathed in sheet aluminum. I originally wanted this to fill in the gap between the original back door and the floor. The pipes were 1 inch diameter for the same reason.
My uncle's framing to hold the sheathing and other aspects of the back wall in place.