Thats probably partly what my cabin cruiser hardware was made of. I had to polish it clean all the time to keep it from pitting or corroding. I always though about those things when I got into an electrical storm as they become superconductors at times. If its isolated, or coated with something like this one metal hood I have, it would be another thing. Although it does get a little warm, even with just pc's in it. I thought of 2 more disadvantages to aluminum. In a marine environment, it will be basically a conductor like a battery cell. Whereever the salt water comes into contact with all that electrical device of the hood, it becomes a cell. That will happen by aerosols from the tank. Without sacrificial anodes, the life of your ballasts and other equipment will be shortened. There is really no good way to apply sacrificial anodes without serious risk to the tank. And in an electrical storm, its a superconductor. In 9 years I've been hit 4 times blowing surge protectors, chips off my computer boards and arching across the room and blowing ground fault outlets. I am thankful that my hoods are combinations of wood, plastic and painted metal. If you coat the aluminun so that its isolated completely, it would be different. Still leaves possiblities for corrosion if chipped, but, not bad as a large uncoated aluminun hood would be. Since you are in-wall, with a room behind, why not use a lightweight frame with reflectors held by wires or lighter framing material? Wood can be very light wieght. A hood does not need to be 3/4 ply or made of oak to be effective. And with that room behind the tank, why make a hood at all? All that does is trap heat providing that problem to deal with. A frame to hang reflectors and lights from is all you really need isn't it? If its exposed, then a shield of 1/4 laminated oak on the front will not be heavy. An oak veneer over ply, sealed with acrylic or something would not be heavy. Actually, an entire hood can be made from that and with the proper framing is light and stong. I have 2 hoods made from some kind of hardboard with epoxy over it. Its very light, even with fixutres in it. Geeze that aluminum hood in the picture above would get really hot, sinking the heat into the thak below. I can't even imagine it. He'll need a huge chiller and better not touch the top after its been on all day. I have some large outside work lights with metal housings. Can't touch them after a few minutes or I get burned. If left on inside, they are likely to cause a fire. Looks like he has a whole bunch of halides inside that closed metal hood above. Looks really nice as well as dangerous to me. If you do something like that, make sure you ground it. One of the rules I have with my tanks is to avoid as much metal as possible as the ions always find a way into the tank.