Today I got down to the real sealing work. I riveted on the tank bottom stiffeners and the drain. Here's a pic of the left tank.
And a closeup of a stiffener. Basically, the process went like this: Get everything ready. Mix up some proseal, 40g of white gunk and 4g of the black catalyst seemed to be the perfect amount for the stiffeners and drain. Instead of dipping the rivets before insertion like some people suggest, I simply dabbed a bit of proseal on the rivet dimple in the skin, then I went back and inserted all the rivets (probably not any better in hindsight). Put on the rivet tape (since these are all back-riveted) and flip the skin over. I put big globs (pea sized) of proseal all around each rivet. Then I installed each stiffener, but the trick here is to set it on the rivets about a half inch off of the holes and slide the stiffener across the tails to wipe off the proseal on the end. Then when the holes line up with the tops of the rivets they are (pretty) clean and the sides are cleaned when they slide through the holes. Press them all firmly down and start back-riveting them. After riveting the proseal spread nicely out the sides of the stiffeners and I finished up by slopping enough over each rivet to cover the shop head. I'm still deciding if I really want to make 'fillets' all the way around the stiffener... The only thing I'm trying to seal here is the rivet hole, and I think the triple coverage of dimple, back side of rivet, and shop head is probably quite sufficient. I suppose another layer of protection can't hurt, but I think it's unnecessary and would just add (however little) weight. I will probably do the fillets around the ribs, as the installation of them doesn't lead to such full coverage of the rivets crevaces with the sliding and after-mating installation of rivets...
And here's the right tank.
