Same here dude, i have no experiance with resin and fiberglass and stuff although I want to learn REALLY REALLY BAD. But to answer your question I personally don't see what the point would be to fiberglass the inside. I have not made many boxes so I am not a proffesional but I don't think it would really affect anything. MDF is pretty nonbreathable (i think?) and silicone is a great sealant so fiberglassing the inside just seems like a waste of money. That is just my thoughts though, you should prolly wait for the pros. If you do try it and ya hear a difference let me know
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