Soon to Fiberglass my doors, not sure exactly what to do

Okay so im tired of having crappy mids and highs and almost no bass without overpower the spakers, coming from my rigged door speaker setups.. I plan to fiberglass the speaker hole thats in the actual door and size it so my 6.5's and tweeters to fit perfectly.. Call me a noob but when i do this should i seal every hole in the door to keep the midbass in the hollow of the door? I was always confused about this and id imagine sealing off the entire door would cause you to lose alot of bass, but according to alot of people thats not the case, so any suggestions would be great =D. Ill be getting started this weekend so i hope to get some good suggestions soon!