Not cheap, but 3M security film is pretty effective:



Combine this with a couple Sliding Door Security Bars (one high, one low), motion-activated lighting, and a loud alarm and I think you'd be safe from anything short of a deranged madman with a chainsaw.
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2010 Jeep JKU Rubicon | 35" KM2 & 4" Lift | Skids | Winch | Recovery Gear | More ...
'13 Wheeling: 8 Camping: 6 | "The trail was rated 5+ and our rigs were -1" -Evan@LIORClub