you want an alarm that turns on your front headlights full beam as well....that annoys joe punter along the road who will notice as they will want to moan about your headlights.....then more people will notice.....also there are cheap smoke generators that pump the cab and back full of dense but harmless smoke making it impossible to see any tools to steal...as for any vulnerable wiring that might be reachable from the engine bay or underside on any vehicle, I would cover it with metal lined copex, which will sicken them as it will take at least a good few minutes to cut through...
I wonder if it would be ok to fit a bright strobe fitment (12 volt) to the roof of the van as well, that would put off a good bright flash just like an alarm wall box.....chase them away....theres also Hard drive based mini CCTV recorders available, full unit about £120.00 I deal with a company called cricklewood electronics and they have all that kind of stuff, sometimes maplins have vehicle recorders in as well.....get some CCTV window stickers from ebay to make this known as well....theres ones for the inside corners of van windows...