Be careful with proseal and no gasket
I just want to throw out a word of caution on going with proseal only on the tank access panel.
My plane is 10 years old now and I've had both tanks off several times every few years to seal a leaky cork gasket. I used cork and a lot of fuel-lube and cork and proseal on each sides, but they eventually always leaked. The last time, I decided enough was enough, and I read the threads about using proseal only, so that's what I did. I sealed the access panels using proseal, tightened down the screws, and put the tanks back on yet again. 2 years later, the tank is leaking (but not at the gasket, this time) so I need to get the cover off (or maybe not, more on that later).
I've now been working for 2 weeks trying to get the access panel open. I'm using poly-gone gel (which dissolves proseal very effectively) but I still can't get the proseal to let loose. Probably because the layer is so thin because I tightened the screws when the proseal was wet. I can't get ANYTHING between the tank rib and the access cover. (not a scraper, not a plastic knife, not even dental floss.)
I would not recommend this **** to anyone.
I have already cut one (several more to go) access panels into the back baffle and I'm even working at it from the inside too.
At this rate, I might just leave it alone and instead create a removable panel in the back baffle in the first bay.
I now found a different kind of proseal that is "less sticky" and can be used for removable panels. That is what should have been used here... not the "real stuff" that is used to seal the tank.
The more I look at this I wonder why there is an access panel on the inside rib at all. It seems to me the best spot might just be the back baffle and use a solid inside rib instead. (I'll post more on this idea in a separate thread)
So, beware. Don't use normal proseal on anything you ever want to remove without destroying.