Rai mentioned one of them doing something worthwhile, or at least more worthwile than in BB-10
Anyway, my trial run of reinforcing a Tornado Attack stadium was a total failure. I overfilled the foam, couldn't clean it up properly to make it all level - it was much stickier than I expected, had to wrench the stadium off, hopefully it isn't badly bent, but it sure is a mess. Ran out of gloves, used about 100ml of acetone-free nail polish remover (which didn't damage the stadium thankfully), got filling foam on my hands and then nail polish remover in a small cut when trying to clean it off, and lastly the foam didn't dry thick/hard enough to provide much protection for the walls.
I think I managed to salvage the stadium, but I wasted my spare board and can't really re-try with the same stadium before I do the proper one.
I think when I do the actual one I'm going to tape the inside corners, layer the underside with aluminium foil and then just use plaster of paris or something similar... Alfoil should provide a little bit of "spring" to prevent damage to beys or whatever, and the plaster of paris should provide protection... And then glue the result to board.
I was just completely unready for the mess... My hands stink of the nail polish remover too, and feel very dry.
EDIT: Turns out despite the can indicating the foam is easier to remove when wet, it turns out it comes off way easier once it dries up, I pulled most of it off the stadium and used a scraper to remove it from the board (though there were a few areas where I guess it sunk in a little where it pulled off some top layer. Stadium is undamaged, the bend only affected the corners at the base of the stadium and it still sits flat. The air holes I put in the sides to allow air to escape are annoying but I have two rolls of duct tape lol.
This means I have another chance to experiment (using a different method, stuff expanding foam).