I had a Viper alarm installed last year. It's a pretty good system and includes an interior motion sensor.
I don't know where you call home, but if you're near Southern California I highly recommend this place
in Upland. Steve the owner is very knowledgeable and can put together anything you want. He is very familiar with RV's and customized a system to do exactly what I wanted.
2005 Fleetwood Providence 39J
CAT C7 350, MP-8 Programmer
My wife does all the driving - I just hold the wheel...