My POPUP is so easy to get into by just slipping your hand thru the window flap velcro and reaching inside and unlocking the door haha...
I do that alot when bringing in groceries etc... easier than sitting things down and looking for key...
Then on the other hand if you make it so secure will just make them mad and they will steal your whole rig...
I'm rigged with motion detector lights on both sides of my off-road popup but if you aren't around that just gives them light to see what they are doing I guess...
Best defense I have found is everything out-of-sight and anything important to me goes where I go in my truck.
Arming yourself is a two sided sword as well...
We have a large dog bowl outside with the name KILLER painted on and the end of large dog chain laying close by. Always have a police scanner going inside... Seems to work for us... We really have never had anything stolen from us that I know about in all my camping years... The RV group sort of sticks together for each other...
Never really camped much alone in a camp ground - Have done alot of tent/back pack camping alone on the Jeep trails in the high country of AZ years back.
Just be aware of your surroundings is best practice I guess
I love my OFF-ROAD POPUP camper

Roy Ken