You don't really need "marine" speakers for your speakers to be water resistant. All you need is a speaker whose cone is made from polyurethane, mylar, etc. with a butyl rubber edge around it and you'll be fine. It is really only speakers that have a paper cone that are suceptible to water damage. Most aftermarket car speaker cones seem to be made from polyurethane or mylar so you shouldn't have any trouble finding speakers that will be fine if they accidentally get wet.