Not your first worry, bro. Your FIRST worry is where the heck the RV is parked.
In some states, when it's STATIC (and hopefully "hooked up") in an RV park or on your own property, it's your home, and the loaded guns therein are treated as being in your domicile. Most places, when it's on the road, it's a motor vehicle, and if you're not legal to have loaded guns in your car on that turf, it's not legal to have them in the RV, either.
CHECK STATE BY STATE, UPDATED, and have downloaded hardcopies of any law that authorizes the loaded guns WITH YOU in the vehicle.
Remember that IN SOME STATES, EVEN WHEN IT IS PARKED, IT IS !!NOT!! CONSIDERED YOUR DOMICILE AND MAY !!NOT!! BE LEGAL. A good friend of mine learned this the hard and expensive way in New York...
OK, to what I would consider the second concern, and what you asked about: As you've already pointed out, distances will be short and space will be small. If you're asleep when the intrusion comes, there won't be time to go for a long gun. If it's legal, go with a handgun, already on your person if that's legal.
No RV is a bullet trap. (Neither are most homes, it's a matter of degree.) I'd personally be going with a handgun round designed to stop in the human body, since that's likely the only backstop you'll have. Seriously, try to park where the primary point of access won't have innocent people behind it in your line of fire...an option that the RV dweller might well have more often than the urban dweller.
Hoping this has been of some help,