The jl marine amps still suffered from gain pot failures with humidity present. Fosgates, power supply shorts.
If all your exposed fasteners in the engine bay look clean , esp the merc fuse junction by the starter , then go for it . If not , then I would relocate to dry area, if you want reliability.

Get a bigger amp than you need and it won't work as hard = less heat so it won't overheat in a compartment

agreed... My subs amp is overkill and bilge mounted... No problems. The JL amp for my mid/highs is not located in a well vented area and up against output demands. It causes me grief sometimes. Go big or go home

I've roasted a lot of amplifiers.
Each and every roasted amplifier was damaged by heat.

I would SERIOUSLY avoid installing in the engine compartment. Even if you are running "marine amps", that's not a USCG rating that they are spark proof. Now, I don't expect a spark out of ANY amp, automotive, marine, or otherwise. Typically "marine" electronics mean the circuit boards are coated in something. Well, guess what that coating does? It retains heat. So now you are creating a perfect storm of how to destroy your amp; and now potentially cause a spark and/or fire. Where? In your engine compartment where you don't want sparks or fire.

Under the back seat may not be so good either, since many of us have our fuel tank access ports there? Why not here? Well that's self explanatory. Yes, batteries and inverters/chargers are installed here often too, but why multiply your risk?

Install the amps somewhere in the cabin. Run a single BIG 0-AWG cable to your amp location, and put a capacitor in there. I liked the Rockford Fosgate Digital Capacitors for this because it's a nice clean install, AND its a power distribution block, where you can break out 4-AWG cables to your amplifiers.

http://www.ebay.com/itm/Rockford-Fos...-/151450492782