Just put all your music on mp3 and get a decent head unit with USB input for a thumb drive. That's what I do on my boat, plenty of music in small package.
My 460 truck has a head unit that plays MP3 off CD, many more songs on a disc in MP3 format... Though I've had the same disc in there for maybe 5 years now? IDI truck came with some off brand (Panasonic?) newer looking head unit with no CD, no MP3, no USB, just a headphone jack input and AM/FM, so it stays on FM on the one station I like. Some day I'll put a nicer basic Alpine unit with USB input, but I'm not picky enough to be bothered yet.
My 460 truck has a head unit that plays MP3 off CD, many more songs on a disc in MP3 format... Though I've had the same disc in there for maybe 5 years now? IDI truck came with some off brand (Panasonic?) newer looking head unit with no CD, no MP3, no USB, just a headphone jack input and AM/FM, so it stays on FM on the one station I like. Some day I'll put a nicer basic Alpine unit with USB input, but I'm not picky enough to be bothered yet.