Greetings all,
I've just finished my DIY system using all your advice. All the "usual" items like MR16 bulbs, JC Whitney lights, Xenon tail flasher, etc., but thought any recumbent riders searching through might appreciate a look at my battery box. Probably only works for an LWB, but there may be other creative applications outside of mine.
Main material was composite outdoor decking material made out of recycled plastic and wood chips, and then I borrowed a router table from a friend once I sketched up a design and more or less machined out the pieces by hand, and it came out better than I hoped. I'd planned the decking material as an easy way to prototype, and then make some final adjustments and find someone at work to beg to make me one out of aluminum, but it works well as is so I'm going to pile up a few miles and see how durable it is. The decking material was great because it chips like plastic instead of dusting like wood, so I could work inside without choking or coating everything in site with woodfilm.
Other interesting tidbit was the dust and moisture proof caps for the toggle switches. No real need to be absolutely waterproof, but they are insert molded elastomer over the regular lock nut and do a good job protecting the seal and the switch. Since this is more or less a permanent mount of a 7 A-h SLA battery, I put some charging posts through the back and just clip onto those with alligator clips when I return home after a ride.
Many thanks to all who posted earlier, all the information in the thread made a great read and an easy choice for what to do. I'm an incredibly slow planner, so you probably saved me an entire biking season.