Fuel Cell Install

My buddy has an 85 Cougar we are going to put an 8 gallon fuel cell in. Heres the problem, someone told us that we have to cut a hole in the floor of the trunk so the two lines and the hump thing can hang outside of the car. Ive never done this and have no idea why that has to hang out. Then someone else told us we could just build a frame to go around the bottom to pick up the hump and make it sit level. Once again dont know. Any help would be appreciated, thanks,

Josh