The crappier your vehicle is the better - in your case too late judging by your website ;-) The more sponsors stickers you have the richer you look - though that applies more to attempting bribes perhaps.
Anyway, strong bolted on padlock harsps are the way to go - the standard landy door locks provide no obstacle - you just stick a screw driver between the handle and the body work, little bit of elbow grease and you can open the door.
Mine are by a company called Corbin, a Black and Decker company - Footloose and others sell them. (about £12.50 each I think - might have a pic ) Then just get padlocks with all the same key and your away. Sleeping in the rooftent without decent locks will mean you will get broken into - has happened to quite a few people.
Worth getting a Full Metal Jacket or similiar as well. Locks up your driving pedals (see
The Expedition Specialists or google - take extra keys) and provides some piece of mind.
Also worth putting in some switches - such as your fuel pump wire - and you should have an easy to reach battery cut off switch as well.
So thats 3 things to overcome before they drive away. Also, park in gear with the hand brake on - harder to tow it away then.
You can get the stick on window protection - works well but bloody expensive.
Everything on the outside has to be bolted down and padlocked.
Oh, and never leave the vehicle unattended unless 100% certain. If you must, plonk a street kid on the bonnet with a lollipop and promise them more if all is well when you get back (girls are best, or brothers and sisters)
Never leave anything in sight such as your gps - have a piece of black cloth to cover your stereo - prevents dust as well.
Thats enough - no more coffee for me today...