Installing a black tank in a 1967 Aristocrat LoLiner

First, I cut out the metal belly pan a couple inches inside where I was going to cut out the floor.  I think I just got under there with tinsnips. Once that was done, I bent  the metal down and cut the plywood, being careful not to damage the sheet metal.

I saturated the exposed plywood edge with thin epoxy, then added butyl tape.

Then I bent the belly pan metal up over the exposed edge.  In this picture, I think I was inserting a spacer block into a gap between the floorboard and the frame.

Just out of an abundance of caution, I wrapped it with Gorilla Tape.  Not sure if there's a long-term benefit, but it's been ten years since I installed it...

I didn't really get a good picture of the next step, but if we jump ahead a bit, you can see the white stripe at the bottom of the shot.  This is angle iron that bridges the gap and supports a piece of half-inch exterior plywood, which will protect the bottom of the tank.

There is another piece of angle iron bolted to the frame on the inboard side.  These two irons support the weight of the tank, and both are bolted to the frame.

Here you can see the back end of the angle iron with tabs welded on to provide a place for the bolts.  I have enhanced the picture to highlight the weld in pink.

I made my own tank using a plastic welder from Harbor Freight.  That's a whole other discussion... The notch is for the P-trap on the shower drain.  If I had it to do over again, I'd ditch the shower trap.  Not needed in a trailer, since RV park hookups have built-in traps, and my shower does not drain into the black tank.

I framed up the bathroom floor up to its original height. This plus the fact that the tank sits down at the bottom of the chassis gives adequate height for a nice deep tank.  With the notch, I think I figured it was about two cubic feet, or roughly 15 gallons.  Lasts me about a week.

Here's another view of the finished framing.

New bathroom floor.  I also soaked it with the thin epoxy.  Actually used this on all the trailer framing because I had found so much rot in the old wood.  It's called Clear Penetrating Epoxy Sealer (CPES). You can look it up.  Might be overkill, but it made me feel better.

Here's the front end of that angle iron that closes the gap, showing the welded tab on that end.  In the back you can see the shiny bolt holding the inboard angle iron.

The strap under the plumbing is there to protect it from road hazards.  I found the need for this the HARD way.  (Don't ask...)

Back side of plumbing seen from under the trailer

Finished bathroom floor. Here you also see my first attempt at a greywater tank.  Just for the kitchen sink.  I later replaced it with a 20-gallon tank under the floor that also served the shower.  A subject for another time...

I cut down Armstrong vinyl tile using a sharp carbide table saw blade.  For the main floor, nine-by-nine.  For the small bathroom floor, six-by-six.