First I hosed down the corrugated steel panels. Sometimes it is advantageous to wake up in the middle of the night and mull things over in your head as you try to get back to sleep. Last night I realized that I didn't have to worry about completely sealing the corrugated steel panels to the wood foundation sides. They exist in the foundation "sandwich" largely to provide a durable guard against road debris, so if I were to stretch a piece of heavy-duty plastic sheeting (like a 3 mil paint tarp) over the foundation before securing the foundation in a few spots to the metal panels, the plastic would seal out any moisture regardless of whether the "bumps" were flush with the wood or not.
Next I moved on to the shower pan and shower mat. Now that the joists were in place, I found that I did not need to double up on one particular side of the shower pan and could use one joist alone to support the sub floor AND secure the pan - this also results in less foundation weight! Keeping weight in mind, I also stepped on the bathroom scale (ugh!) both with and without the pan and was pleasantly surprised to find it weighs only four pounds - I suppose since it was made for RV use the manufacturer was much more attuned to this issue. So far I've calculated the foundation sandwich - metal, insulation, wood sides, hardware, plywood sub floor, shower pan and mat (see below) to be right at 260 pounds. It's all going to add up quickly, so I'm trying to be very careful every step of the way.
My plans call for the shower pan to be recessed into the foundation and a teak shower mat to float above it at floor level, allowing water to drain through to the pan below, all while appearing more like an actual floor (or door mat as the case may be, considering it is placed right as you enter the house from the front door). Lots of Internet searching found a very affordable mat ($45 with shipping!) that was just the right width to span the shower pan in one direction, but just a bit too short to span it in the other. However, I figured I could saw it apart and space the slats a bit further apart. When the mat arrived Friday, I was pleasantly surprised to find it wasn't just tacked together, but rather screwed, so with some unscrewing and a bit of hammer tapping to loosen the glue, I now had 14 teak floor slats at the fraction of the cost of purchasing the raw lumber. They will of course need to be reinforced at some point with cross rails, but I may be able to re-purpose the ones I removed in a new configuration - I'll just have to do more middle of the night thinking I suppose to solve that problem!
All in all, it was a short work period this weekend, but a satisfying one.