I am installing an engine that requires a 3/8 in firewall. The firewall installed is only 1/4. What is the best way to increase it to at least 3/8? I do not want to add to the outside if it can be avoided and on the inside I will need to cut the size down to get it to fit between other fuselage structures. Also on the inside of the firewall it is not very smooth and I will have to do some sanding in hard to reach area's. Can I add fiber glass to the inside this would be easy if the fiberglass is strong enough to reach the same strength as a 3/8 firewall. Thanks for any advice.