The one main rule of vehicle and caravan security it to make your van more trouble than the others available, Sorry but its true. Think about it for a second, a thief has the choice of 2 identical vans, one is fitted with an alarm. EASY CHOICE.
So, with this in mind consider the following.
If your van is in a storage yard get it moved so it is surrounded by flashy caravans, if yours is the flashy van, get it moved near others the same, then think what you can do to make it so that it is not as "selectable" as the others. Add more security than the others but make sure it is visible. no use having an alarm if the only way to find out is to break a door, the damage is done before the alarm works.
Next, if you store your van empty, leave the blinds open. Why? well if the thief can see it is empty they will look elsewhere for goodies, leave the lockers inside open, show them they are wasting their time.
Security!
Always fit both a hitch AND wheel lock, use these in storage and on site. Also, try to get a hitch lock that can be fitted while towing, useful if you have to leave the van for 5 Min's on route. Make sure the hitch lock is either designed for the hitch (ALKO) or covers the bolts that fix the hitch to the chassis. Always use a wheel lock that covers at least one wheel bolt and try to get one which is marked "sold secure" as these are tested. Try to find locks that do not use padlocks as these are easy to cut with a petrol grinder. Use locks that insert into openings and are anti drill where possible.
If the rear steadies on your van are lockable then lock them. either with a special lock or look for the local "BIKESAFE" event and go there and buy a magnum chain and lock for a motorbike. these are cheap and VERY strong and use the same lock as the ALKO steady lock.
Try to paint your locks bright red or yellow, make them so they can be seen so that thieves see them quickly and you see them to remind you to remove them.
Alarms
Use a dedicated caravan alarm as these have internal batteries for use when the caravan battery is flat, they recharge from the caravan battery. if you have a solar panel, set it up in the van with a roof light open to add a little charge into the van battery while in storage. Place any stickers from the alarm on the door, front side windows and the a frame if you have enough.
If you store your van at home or if the storage place will allow, fit a motorbike anchor. this is concreted into the floor and fixed to the van by a chain, use the magnum chain from above or get any welded link motorbike chain. again, make it bright so it can be seen.
Now here's an odd one. Clean your van and polish it BEFORE you go away in it and put it away dirty. the polish will make it easy to clean when you get it out again and a dirty van is less desirable than the nice bright new looking van next door.
I hope this help someone and remember this, wherever your van is, stand back and take a look. is it harder to pinch or break into than the one next door? Is it less desirable?