I just finished my custom box and i was searching around and saw what to use to seal the sub on the box but i lost it and i cant find it, i think i read something about weatherstripping or something but im not sure, so what are the suggestions on what to use and how i do it and also if i can just buy something somewhere to make it easy and quick please let me know

A double sided foam weather stripping tape works great. There's a ton of it in all the hardware stores this time of year, it is in the same area as the window insulating kits.