Great solar charging info and tips in this thread, thanks for starting.
I would sure look to 0.032” AL plate or some 1/8” ABS as a backer, or even a combination thereof to create an enclosure. Lots of AL shapes and bar to be had on ebay, Amazon, or the hobby store.
No long term usage yet, but my solar rechargeable flashlite project seems to work fine with 100% silicone window and door caulk, for securing the mini solar panels to an AL backplate.