I would not expect any difficulties, at least none that aren't obvious (like the new one being half as large), assuming you're putting in a car radio. Do check to see if it's likely that there's sufficient depth clearance; a CD player needs to be relatively deep compared to a tape player. I think most RV radios use the same type of antenna connector as car radios (which is not the same as most home stereos use).
I'd also suggest at least thinking about getting a unit with basic bluetooth support; it can be mighty handy to play back sound from a cell phone or iPad or whatever through the stereo.
If you were to install an automotive DVD player, there may well be some trickiness involved in getting it to display as they aren't legally allowed to show the movie (when in a dash) while the vehicle is being driven. They have a lockout typically tied to the parking brake switch, and many require some specific sequence of applying and releasing the brake before turning the screen on, so it's not just a matter of wiring that to a constant ground or +12V circuit as appropriate. A little bit of searching online in regards to the specific unit will usually show what, if anything, can be done to work around that. Obviously this won't affect you since you aren't talking about putting in a DVD player.