You're making it too hard.

Drill the holes. Run the fuel lines through. Seal the firewall. Done.

So you get some epoxy on the fuel lines............... so?

You planning to take the tank out every weekend? You don't like epoxy on the first 1/4" of fuel line sticking out through the holes? Is that going to ruin the model?

By the time you need to take that tank and fuel lines out........... you'll want to replace the lines anyway. You trying to save that 6" of fuel line for the 2nd tank you put in this model 5yrs from now?

Get er dun!!