See if filler tube is flat by removing cap,
find a flat plate - lexan, steel, alum, etc, - and cover plate with emery paper or 1500 to 2000 grit sandpaper, and sand the tube barely.
You are trying to find a brighten area about the tube with no dark spots about the circumference.
Not flat, leaks.

Another suggestion, check tank venting to canister.
No venting, pressure build-up in tank due to road heat and could push fuel out the cap from fuel trapped in tube.