The most comfortable ones have the bottom pad that pulls out. These also cost the most but we'll worth it. This experience is from 3 different brands I've sat/rode in.
I'm not happy with how well the corbeau's covers seem to hold up. 2 sets installed in 2 rigs and the piping is falling apart...
Buy a better cover.
I only install casted covers though. The fabbed covers will most definatly hit a TJ fuel tank. If this isn't in a TJ, get whatever you want.
The best cover I've done is a crane cover. Cast steel one though. Crane sells two different castings.