Martin's OTR, Is your current radio a standard one DIN size or a 2 DIN? If it is a 2 then look at the 6 CD changer types. A single is just a single CD type. Either way the only difficult part is running the antenna block to the outside. I guess some sets come with the combination antenna and it is still a pain. It's not hard, it's just a pain.
There are as many adaptors as there are car manufacturers. It will convert your RV's cable connector to the cable connector for the radio. It makes it a lot easier as there is no splicing, the cable connects to your existing system.
If you have to enlarge the mounting hole in the dash, there are molded boxes available on ebay to put in the hole and then mount your radio in the box.