I've thought of the cut towards the top of the tank, versus the bottom. Ruled it out, as it's just extra work to clean it all up. Ditto for splitting it lengthwise, top to bottom! As for plastic causing a problem with the fuel... that's what we store our fuel in, in the garages. Plastic fuel cans! My greatest problem, is that when I do my father's tank, I don't EVER want to have to do it again. As such, I don't trust a single damned one of these chemical products out there, it being a false premise to consider 'this' sealer a success, simply because it 'held up' for 3 or 4 years. I do not think the tank is all that difficult... it's finding the RIGHT liner that seems elusive as hell. Jean apparently did his well, but I'd only wish he'd done it 10 years ago and could report it still holds up! It seems easy: make it permanent, or go with metal, aluminum, whatever.
Send me a PM of your email address, and I'll send a pic of what I mean from my earlier description. It's very much similar to some of the guys referring to lining as 'tabs'. Same concept.