I use a loop of paracord to hold mine closed. From inside it's easy to slip the loop and open the door but anyone pulling on it from outside would hopefully make enough noise to wake me. Not much I can do about the window screens* but I'd do my best to render any arms coming through in the night into stumps.
*I've actually thought about mounting a bar or something across the opening but for some reason I really don't like the idea of having only one way out.
05 Tacoma TRD, SR5, V6, etc
1978 VW Westfalia
2007 Suzuki DRZ400s
You know, Hobbes, some days even my lucky rocketship underpants don't help. -Calvin