I used to run all marine grade stuff in my boat. I had 2 marine JL audio amps, marine sub, marine head-unit and speakers and had nothing but problems with them.

The sub I had was a Marine rockford fosgate 10" that was directly behind the drivers seat drilled into that small fiberglass section between the driver and the backrest for the seat behind the driver. The first one I had blew within 2 months and the next one blew within 1 1/2 months.

Since then they installed all NON-marine parts except for the tower speakers and speaker around the boat. Headunit, amp, and sub (that is in open air) are all non-marine and I have not had a problem since!! It has even rained on the non-marine sub, I was stressing about that though, and it still work perfectly.