Do a search for Hawg Wired, their speakers and amps are expensive but the sound is fantastic. I think this is a case of you get what you pay for. I am currently having them installed on a new 08 SG.
I swapped out my crackeled factory's withsony 5 1/4's any speaker in this size will work. The main thing to look for is sound quality. I went with a pair of 3 way to get a full range but for the best noticable highs at highway speeds. If this helps any.
Your quite welcome. That's what this forum is all about...as there are some great people in here with tons of knowledge. The JBL's I installed and of a poly design, and although they are not classed as a true marine speaker, they'll hold up to most anything you can throw at them as the entire design is engineered for multiple elements and climates. I've already doused them twice with a car wash wand and I am not at all worried. Their a pretty solid speaker and should last for years.
I have HOG Tunes on my Classic and the wife has them on her SG. We are happy with them, and they are abig improvement over stock. The company is also great to deal with, and you get a discount if you are a forum member.