I used a peice of 3/4 particleboard to mount my bottle to and now the top wont go on compartment very well, how did all the C5 guys do this to make the top fit without alteration.

 

http://www.860performance.com/Car%20...tte---main.gif

This all fit under the top cover.
Its kinda tough to describe but what I did was take 1/8"x1.5" steel and bend 2 of them up to span across the pocket. You can see one of them near the bottle valve. The other thing I had to do was to take the bottle apart and modify the draw tube since the bottle needs to lay sideways, otherwise the blow down tube would stick up too high.
Hope that helps.
Vinny

 

So are the brackets mounted to the bottom or side of the compartment.

 

The steel strips bolt down on the shelf on each side. The heated bottle bracket bolts down to the steel.
The picture is kinda dark, but the steel bracket is seen kinda behind the blow down tube in the picture.