Most secure motorhome?

I believe that at least one exit window is mandated by DOT. The windshield can be accessed without too much difficulty. An alarm system is not a problem, you can have a competent alarm company monitor the windows, the door, and even install a motion sensor. These systems can be monitored 24/7 with a cellular system. You could bar the window and put a screen behind the cab, similar to check cashing vans, making access to the rear extremely difficult. But in reality situational safety is more important. Stay in a safe campground in a safe neighborhood. You can check with the local law enforcement to see if the neighborhood you are choosing is relatively secure. Campgrounds are full of people, increasing safety. You bigger concern might be travel to and from work. Parking lot safety, commute safety, and shopping safety.
Just be careful and get professional advice before making your home too secure. Bars on windows, even in brick homes, and trap you inside as well as keeping rescuers out.