Yip indeed surely they dont cost that much to have fitted as the lock is not that expensive ??? Don't think mine cost all that much as it goes, you can also get slamlocks that deadlock when door is shut but you cant fit them to all doors as they only open from inside ?? not great on a camper what you need to do is strike a happy medium where its harder to get in but not to the point they simply pan a window Common sense dictates that all valuables are well out of sight obviously sadly with mine being a motorhome i have extra worries in that department to the extent that whilst we have a manufacturers fitted safe under one of my seats i far preffered my original idea of it opening into the footwell and not the rear that way you had to get the door opened before you could get the safe opened, and with deadlocks of any description that is a kind of hard task, so even if your window is panned they still wouldnt get the safe opened as the door is larger than the doors aperture between it and the door where as rear facing safes can be seen through the side window and opened far easier, my last van had the later design with the deadlocks making it as safe as possible in most circumstances that a car thief may operate.
The secret is to be safe but not paranoid to the point that you are always worried about leaving it or it will just ruin your enjoyment a much better bet is to have clealry visible locks thus they will in most cases simply move on to the next not so well secured one in the row..... a phylosiphy that has always worked for me anyway....
[A wee tip if its double glazing door locks keep the fronts of said locks smeared with a little grease or vasaline why? simple to stop them tarnishing [another T4 Club Top Tip]]
none at all well excludung a toilet access that is !!! the way to go no backdoor then you dont need to choose have a toilet and shower instead like me 
provided fitted correctly be rust free. 