How important is sound quality to you? Do you have room expand the diameter of the speakers to 6 1/2, 7, etc.? If you don't mind spending some coin, and making some mod's, even if you have to add a spacer on the outside wall to allow for deeper speakers. Then the a look at sites like Crutchfield. For example, they have a JL two way (and unless you're going to separate components and an amp, two way is what I'd recommend). Like:
JL Audio M770-CCX-CG-WH 7.7" marine speakers with white "Classic Grilles" at Crutchfield.com
This is 3 3/16 deep, so a spacer the side would be needed. It has a decent crossover, and is relatively efficient at 91 dB. Good quality construction. My BIL has these in the cockpit of his fishing boat, and they put out some good sound.
But, it all depends on how important eh tunes are to you, and how much PITA you want to go into for an install.
Another option would be to abandon them, and go with one of the rechargeable bluetooth speakers systems, that you set outside when you want to have some tunes.
Same BIL, has a pair that he used inside an older trailer, and then moves outside when he wants the tunes... Paired with his phone.
Best of luck on your decision choices!!
Smitty