Got my tank repair kits from Vans and started on cutting the holes in the back baffle. I'm a little concerned now that the leaks potentially extend across three bays. My attempt to proseal from the outside likely extended the apparent limits of the leak, but with all the proseal removed it still appears to leak from the ends. Just to be safe I will seal all three bays. I need another patch kit then.
Cut the holes a few different ways, none is great. I tried drilling a perimeter of holes and then snipping out the skin between. This leaves a very rough, almost saw tooth edge, that quickly eats up the sanding drums I was trying to use to smooth it. On the second one I used a carbide bit in the dremel to just cut it out. Came out a little better but time consuming.
I also purchased a $40 borescope for my phone to get some visibility on the repairs. The existing proseal beads look pretty good to me, but they apparently leak. I'll just lay a new fat bead in there and cross my fingers.
10/23: last night a strong gust of wind blew my tank off the table it has been sitting on outside. It bent the bottom skin a bit in the corner, but I was able to bend it back by hand. Hardly noticeable. Lucky.