+1 for removing the access plate and doing the repair from inside the tank. You will feel better knowing it is not a patch from outside the tank.
You may want to consider the careful use of a heat gun on the access panel. The heat will help soften the proseal ... making it a little easier to get a blade, putty knife or tool of your choice between the access panel and tank body.
RV-12 Wings, Empennage, Fuselage, Finishing, Avionics and Powerplant kits all completed
Dues paid until September 2019