How can I best waterproof speaker fronts for boat use?

I have found four Wharfedale Pro Titan 8 mini PA speakers that I am going to use in my boat for fun. I take heavy metal fishing trips with the boys every now and then, and the 6x9 JBL marine speakers are a bit to weak to really blow the fish out of the water. :ROFLMAO: This is how the boat looks with the front 6x9:


There are a pair of the same type in the rear, barely visible in the back on the closeup. These new speakers are only a little bit bigger than the 6x9 with boxes, but handles much more power. They are meant for outdoors PA use, but not with a direct, heavy water spray like heavy blowing rain or spray from using the boat in 30 knots in waves (they are IP45 rated, but I don't trust that fully).

So my plan is to hang them horisontally under the roof, where the boxes for the 6x9 are now, and build open top 2 mm aluminium sheet boxes around them, bolted to the roof. That will take care of side and rear splash, the problem is front splash for the front speakers, and rain, when the wind comes from the wrong direction and drives it underneath the roof.

I was wondering if it's possible to use alumium sheet as fronts and then have cutouts where the drivers are. But the water resistance is the problem. I would either have to use a kind of a lid and remember to put that in front of the boxes when I dock and remove them again when I'm going out and want some tunes, or find a kind of material that will mostly stop the water from coming in to the speakers. Would for instance a double layer of Gore Tex work for that?
@Addled The boxes won't work, I want aluminium to go with the boat. But a vent grill is a really good idea, thanks! I can probably even get one that can be adjusted so I just close it when I'm not using the speaker! I'll start looking for the right one here in Norway.

@GM Thanks! That can be used as an extra weather proofing!

I'll run with these ideas and see what I can manage.
You have no idea how much ready built enclosures cost in Norway... or anything ready built, for that matter. A box that would fit one speaker would set me back around 300 British pounds, which is more then the speakers cost me. And shipping to Norway is also expensive. I can get the alu sheets for a good price, since I know a guy who runs an oil supply workshop and uses a lot of it. And I'm quite good at putting together stuff like that, I have built and adapted a lot of stuff for my alu boat.