[nsb29]

If it were me I’d try to do one cut but if you have to do too it would just mean more work. The best way to do fiberglass is to taper both sides of the but joint about 20 to 25 degrees scarf tip cut I would do this on the outside of the Box now tape the seem on the inside after it’s taped if necessary reinforce by tapping paint sticks where you need it. Now you can fill the beveled area with fiberglass mesh and Resin after it sets up you can sand it down flush. this is typically how fiberglass repairs are made