I'm just going with fiberglass in the corners with the bluemax over top. No seam tape. My corners are very solid already though. I probably don't even need to do the fiberglass, but will for peace of mind.
You guys have way too narrow a view of silicone... GE Kitchen and bath crap won't adhere to much... but there are literally hundreds of silicone based adhesives from henkel (Loctite), DOW, and Sikaflex - many of which bond quite well to acrylic, polycarbonate, and rubber. Sikaflex 222 I think it is, the marine underwater window sealant is amazing stuff "Will glue snot to an icecube" is the best way I've heard it put. DOW 832 is pretty damn good too, and is fish safe.
Don't know, you'll have to do some looking. Google DOW 832 and read it's datasheet. It will likely work, as usually in the application you're talking about the sealant doesn't need to form a strong bond, it just needs to stick a little bit and then the water pressure holds it in place.