Unless you really beef up the framing around the bed then it won't be very hard to tear the mattress platform off the base.
Most all the framing is cheap 2x2's stapled or screwed together that probably already have a few splits in them.
There's two types of thieves IMO. The one's that are looking for an easy in like a door left unlocked or the one's that will tear open a door to get in. The 2nd version will tear the bed platform up to get it open.
Someone with a cats paw could get into just about any area on or in an RV.