The hardware is fairly cheap to buy. The problem as I see it is the doors are not strong enough to support the hardware without flexing... Building up the door skin so it will support the slam locks is not an easy task... Then there's the issue of mounting the "flange that the slam lock fits into that keeps the door closed. It can be done, but think it through before you start the changeout....
You might want to go to an RV dealership and take a look at just how the slam locks and the support hardware are installed and see if you think you can modify your existing door frame to mount the locks.
It may be easier and maybe even cheaper to just replace the entire assembly with new doors that come with slam locks installed....
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS