Security is always a trade off. You trade usability and aesthetics for security. The question that each must answer for themselves is: What is the appropriate balance? What's appropriate for one, for example leaving an empty compartment unlocked, will likely be wholly inappropriate for others.
There are many ways, some legal and some not, some practical and some not, to improve security. It is entirely possible to reinforce the compartment access door to the point that its "practically" impenetrable. However, doing so only does so much good... The rest of the RV isn't as easily secured. So for instance, you could replace the access door with a solid steel door, but the wall of the RV is made of an thin skin of fiberglass on the outside, thin plywood on the inside, and Styrofoam in the middle. The compartment is probably also at least partially accessible from inside the RV, so they could simply break a window climb in and access it that way. Etc...
So what makes sense? There are a few simple things that can make you less attractive than your neighbors. Some of them are simple and not too invasive aesthetically. Some are less simple and more invasive.
- You can choose from an array of replacement cam-locks with varying degrees of improvement is quality/security.
- You can look at increasing the length of the locking tab on the cam locks, again with varying levels of quality
- As I suggested above, you can reinforce where the cam locks engage. This can be easily done with modest cost and modest security improvement or it can be much more extensive. For simple, just screwing an L channel to the existing door flange and the plywood floor will add a fair amount of security. To take this further, you could add reinforcement under the floor of the compartment and securely screw/bolt the L bracket to the reinforcement.
- Look at the reinforcing the area the cam locks are installed in. You can fabricate a plate similar to what opnspaces suggested. If you search for cam lock mounting plate, you can find them for a couple of bucks. One on the inside with a couple of short screws will provide a modest increase in security. One on each side with bolts through would significantly increase security at the cost of aesthetics. These prevent the lock from spinning in the hole in addition to spreading the force.
- Reinforce the door with some type of wood or metal backing. Again, this will likely come with some aesthetic trade offs.
- Add reinforced locking mechanism or bar only accessible from inside the trailer, assuming you have access from inside.
- Add a locking mechanism that only opens from inside if you have access from inside.
- You could add locking hasps as other suggested, quite effective, but not so aesthetically pleasing.
- As I already suggested consider an alarm system for the compartment and the RV. Hopefully the blaring alarm would scare them away. Most don't want the attention. You could even get something with cellular notification to alert you something has happened. As a side benefit, you could add fire alarms to the same system.
