The problem is that just beefing the lock does no real good and potentially invites more damage as the crook tries to get through. In order to be effective the beefed up security has to be visible to persuade the perpetrator to move 20 feet over to the next RV. So the L channel won't really deter a thief because they are not aware it is even there. And once the attempt is made the guys sense of pride might take over and he's going to get in.
So think along the lines of maybe changing the existing lock to a barrel lock. It visually shows that attention has been paid to the security.
Barrel lockNext use a security plate externally under the barrel lock that stretches across the bottom of the door for a few inches. The link below is just to illustrate what I'm referring to. In all actuality you might have to build your own plate.
Security lock guard plateThen use the internal L channel to beef up the door frame.
The door is still weak, but the appearance is that the door is beefed up and hard to thwart. Hopefully the crook sees the extra security when walking up and decides to just move on to the next RV.