my rockford fosgate amp, powering 2 hx2 12 inch subs will usually shutdown after 30 or 45 minutes when played at full volume. The amp is sealed in the trunk mounted on the backseat split in my civic., when the seat is folded down it will not over heat as long as there is some airflow.

I was thinking about some kind of cooling solution, something along the lines of fans mounted on amps, but havent done it yet.