I'm with you up to the point you're talking about the caulking inside the trunk. Starting with the flange on the body there is an approx 1" wide 1/4" thick gray seal. The flange on the gas tank sits on this seal. Where is the caulking?
The caulking is on the inside of the trunk. Looks like it was applied to the area on the edge of the gas tank flange to seal the area between the gas tank flange and the body.
FYI - when I removed my tank, I first had to take a screwdriver and a few small scrapers to remove as much of the caulking as I could. Even after I did that, I wasn't able to break the seal between the tank/caulk/gasket/trunk by pushing up from underneath, and I'm not a small guy. Then I used my floor jack -- put a 1x6 under the tank and jacked up until it popped free. Without caulk, I would have been able to pop it out no problem.
Edit - if you want, I can try to take pictures of the remnants of the calking on the car or tank. I scraped most of it off, but should be some residue. Let me know.
72 GT Junior, Amaranth Red/tan; 66 Fairlane GT convt, 428, 4 sp; 68 GTO Convt, owner built 455 and TH400; 71 Javelin road race project, owner built 401, T10