Okay, more progress. First, I have reinstalled the toilet, so the shower is complete except for shower curtain and rod:

Next, I completed the plumbing for the drains. Here is the view under the sink. I had to use a green rubber p-trap to allow for insertion and removal of the top drawer. This picture also shows the air vent for the plumbing:

Here is the plumbing under the camper, shown from the left (driver side of tow vehicle). All PVC is 1 1/2". The drain from the sink drops through the floor at the far end, intersects with a tee-fitting to bring in the p-trap from the shower, and finally mates with an adapter to let me use a standard RV hose fitting.

Next up is the plumbing for water
to the sink and shower, upholstery, a battery, and it will be complete. Except for the odds and ends that will always come up.
Also, I've decided not to mount the water heater to the camper, there isn't enough room in the area I reinforced. I will simply make a mount to attach it to the propane tank to be carried in the camper or tow vehicle while enroute.