...first, the shower enclosure from BivouacBuddy.com is not the one on their home page that shows a reservoir on top. Ours is just the "enclosure" without the reservoir. (Click on the "Showers" menu tab at the top of their page to see it.) As such, the top of the walls of the enclosure can go all the way to the ceiling, if necessary. This type of unit is great if you have an external shower system, as the shower wand can be located right over the open top... no need for a reservoir. But this is not the problem.
The solid plastic pan at the bottom of the shower is about 2 inches deep and 32 inches in diameter. The problem lies in their drain opening in the bottom of the pan. It's not round. It's more oblong. And to complicate matters even more, part of it is on the bottom of the pan, while part of it wraps up the side. This is great for gravity draining outside, insuring that all the water goes out right down to the last drop. But it's a poor idea if you need to hook something up to it so that the water drains away from the enclosure.
I have been wrestling with ways to be able to drain the shower pan inside the trailer. At first, I was thinking some kind of fitting, but that would likely involve gluing a patch over the existing hole and creating a new one straight down through the bottom. Any kind of threaded fitting with a lock nut on the inside would stick up and not let the water drain completely. If put through the side, it presents the same problem. And anything glued to the outside would only add a protrusion that would make it harder to store the unit when not being used.
Then there's the issue with the drain plumbing on the trailer. A hole would have to be made down through the floor of the trailer right in front of the couch, with the ability to seal it when not being used. Any drain under the floor just adds to the work of installing it, as well as something extra to get damaged from road debris. The trailer frame is only about 3 inches in height, so that doesn't leave a lot of room to hide or protect plumbing pipes.
Last week, I came up with an answer... one that I believe is a very good one, and that will have everything within the trailer and yet totally out of sight.
First, a small platform about 32 inches in diameter is necessary to raise the shower base off the floor by about 2 inches. Don't worry, we have plenty of extra head room for our height. The platform should have a very slight tilt to it... about 1/4-inch lower on the drain side. The tilt is optional. It would be easy enough to tilt the entire trailer slightly to accomplish the same thing. On the drain side will also be a cut-out to allow a shallow pan similar to a 12 or 13-inch square cake pan, not more than 2-inches deep, to set about half-way under the side of the shower at the drain hole location.
The other half of the drain pan would extend out from under the shower base, so that a small shallow condensate pump can set into the drain pan outside the shower enclosure. The pump can be either 12 volt or 120 volt, and I have found sources for both. The specs say the footprint is about 5 x 12 inches, so it would fit flat in the bottom of the pan (the pan would be the "sump" that catches the water and must be pumped out of). This kind of pump will suck up everything down to less than 1/8-inch of water, and pump in excess of 2 gallons per minute, so there will never be a problem of putting in more water than it can pump out.
The pumps have their own adjustable float switch on them, and will only pump when there is enough water in the sump. They are also a diaphragm type, same as most RV pumps, so they can also run dry without damaging seals. From the pump, a piece of clear Polyvinyl hose for the output would go right up to the sink, with a baffle to prevent splashing, and also enough weight to hold it in place so the water could drain out through the sink drain.
The wand for the shower would be the standard kitchen sink spray nozzle, and a simple spring clip attached to the ceiling or to the top ring of the shower enclosure could hold it in place. It would have to be a type that would allow the sprayer to remain on without the lever being pressed, but those are easy to find at any hardware store. If the original hose on the shower nozzle isn't long enough, it's easy enough to add some fittings and attach a second hose to extend the length, as long as the fitting will fit through the escutcheon fitting on the sink (the part that holds the spray nozzle).
After the Bivouac Buddy enclosure is dried thoroughly, it and the platform stores flat against the back wall of the wardrobe closet, behind the clothes, taking up no more than 4 inches of thickness. The pan and pump can be put away in a cabinet, and there is no trace that a shower was ever there or is even available.
What little bit of water might remain in the pan after showering, or drain back through the pump, can be dumped into the kitchen sink before drying it and putting it away.
Since this is not a shower that would typically be used on a daily basis, this system is completely workable, and very little trouble. The only work is to create the platform for the base, and it doesn't have to be heavy. A framework of 1 x 2's on edge, topped with a piece of 1/2 inch plywood is all that's needed. Leave a cut-out on one side large enough to fit half the pan into it, so that the top of the pan is flush with the surface of the platform, and that's really all there is to it. Everything else is just a matter of hanging the shower enclosure at the top, inserting the pan under the edge, setting the pump into it and plugging it in. That's no more trouble than I have seen in many of the Class B RVs with their "fold-out" shower setups.
With this arrangement, you can take a nice hot shower in the privacy of your nice warm trailer, and have it every bit as convenient as any other small RV. You won't have any mud to drag into the trailer, no worry of critters getting into the shower, and no worry of "freezing your tutu off" if the temperatures get a little chilly outside.
The hot water in our case, will be supplied by a small "under counter" 4-gallon electric water heater, mounted right under the kitchen sink, so any water loss waiting for the hot water to arrive at the faucet will be negligible. But it could also be supplied from any other water heater that you prefer to use, including an "on demand" water heater, or even a portable unit, like a Zodi brand.
For ventilation, our design for the trailer will have a Fantastic fan right above where the shower will hang, so any moisture will be quickly drawn out before it has a chance to add humidity to the inside of the trailer. With two of these fans, one at the front and one at the back, both reversible, it will be easy to have the rear one blowing in and the front one blowing out, which will have the capability of creating quite a breeze in there!