RE: Fuel tank access
The pre-cut hatch sounds like a great idea. I'd think the covering would hold it place, as long as you iron the covering to the sheeting. If you like to iron covering only at the edges, maybe you could just tape the hatch on underneath the covering.
I like fuel tank access, too, but I have to admit that in the several dozen planes I've owned over the years, I've only had to replace a tank twice. Naturally both were planes that had no fuel tank access.