I was really nervous about it since I didn't know what to expect under the floor of the shower stall. The floor of the toilet/shower stall is 2 1/2 " higher than the floor of the trailer. The whole process required that I had a hollow space between the floors in order that the sink drain that I planned, had a surface to seal on. If I had run into a solid support between the floors, I would not have been able to attain a seal. I located the drain in the corner of the shower stall closest to the bed by cutting the appropriate size hole with a hole saw completely through the shower floor AND the floor of the trailer. Believe me, I was sweating! I didn't know what I would find. Luckily, the whole thing went as hoped. There was no support block in the path of the saw, and I had a clear path all the way through. No wires cut either! As luck would have it, the shower stall floor is a 3/4" fiberglass sandwich with chip board in between. The chip board was not good news, but I managed to seal this surface with epoxy so that it doesn't get wet if water seeps into the cavity.(THIS IS VERY IMPORTANT. DON'T MISS THIS STEP!) The reason for locating the drain in the corner was so that I would have a way of holding the sealing nut on the drain so that it could be tightened against the shower floor. I cut a 3/4" slot in the corner of the stall with a hack-saw and held the nut with a pair of vice-grip pliers while turning the pipe with a strap wrench from under the trailer floor. I used a rotary (Dremel) tool to round and smooth the edges of the slot and it doesn't look all that bad. Once the epoxy had hardened in the hole, I inserted the drain while threading the sealing ring and nut on from under the shower floor, through the slot. Before tightening the nut, I filled the cavity in the shower floor with silicone 2 in order to ensure a good seal. Most of this oozed out when I tightened the pipe against the nut. Once installed, I sealed the hole where the drain exited under the trailer with silicone. I have a ten gallon container that I slide under the trailer to catch the water from the drain. This doubles to catch grey water from the sink when we are on a "dry site" for extended periods. The Oxygen has a very small black/grey water tank.
The shower installation was simple in comparison. I started by locating the taps at a point where the water could enter from under the bed. This is lower than I would have liked, but the alternative was running pipes on the surface of the shower stall. Plumbing into the existing water system is easy with "flex-pex" pipe and removeable fittings, although the fittings are incredibly expensive. I located the hand-held shower bracket as close to the ceiling as possible. This ensures that most of the water drops to the floor and little gets on the walls etc.
I have ordered the battery powered shower unit from Coleman to complement the installation when we are on a "dry site" since the Oxygen only has an electric hot water tank. We will simply heat the water on the stove and put it in a bucket for a shower.
If you attempt this project, be sure you are really handy with tools and protect yourself from fiberglass dust by wearing a face mask.