I am not sure about cooling, i had an amp fitted like this a few years ago when i had a cavelier gsi and had no problems with it then.
The back of the amp is not covered there is no back on the box i have made just top bottom and the front. Do you think i need some sort of cooling and any ideas to how to do it ????? Thanks for the comments as for making it, it wasn't to hard just took a bit of time to get the front cut right and it can be removed easily as the bottom is covered in velcro and the top has small right angled brackets on and it just bolts up to the little bolts that hold the parcel shelf supports in place.
As you can see in the picture just need to paint them so they don't stand out to much. But that holds it in plcae really tight and well. :L