In my years of building car entertainment systems, you should never enclose an amp unless you have a circulation system to cool the ambient air surrounding the amp.  That was after I learned not to get them wet.  Although happy's hinged box accomplishes the moisture prevention goal, I would recommend porting the box and perhaps installing a cooling fan depending upon the size of the amp.  Also, remember that hot air rises, so you need to keep this in mind when designing your cooling system.