Odd. I've never had a problem with fuel getting under the tape edge. But I am picky about my brand of tape. I always use Uline brand, I find it has better glue than 3M or some other brands. I do mist the foam with 3M-77 before taping as well.

I did have a couple of wings done with covering basically explode when hit, and I've had taped wings have the foam fracture in to a handful of really big chunks, but stay together inside the tape. Either way, you're going to crash, and the wing is done for the day, but I find having the parts makes it easier to fix , and sometimes you can aim the crash.

When using Ultracote, I use clear. I'm going to paint it anyway, and of the plastic film coverings, white is the heaviest, black is the lightest tinted, and clear is noticeably lighter and I find it easier to work with. (white heat shrink is heavier due to needing more pigment to make an even color. It's not a big difference, but it's non-0). I really like working with the clear ultrakote.

Tape vs covering really is personal preference though.