Hi,
I fitted a Concept Kel alarm [not sure of the model] two years ago to our Avondale Argente [2004] I chose the Kel as this was fitted as standard to the 2005 Argente. My personal opinion of the alarm was that it was rubbish, the fobs were cheap and the buttons were easy to press when the fob was in your pocket, the alarm had a battery back up with an over ride key switch on the unit that could easily be switched off with a paper clip. I am unsure of newer van alarms but our 2007 Fleetwood has an alarm on it with no visible components, a microwave sensor is used instead of a pir, and it seems faily good, but I am unsure of the make.
Try talking to Thiefbeaters, they will give you advice even on products they do not sell and they will know about insurance discounts etc.
I used to be a Thatcham approved installer for car alarms and I was surprised at the Kel alarm when it came, I would not buy another, but the poor quality did match that of the Avondale it was fitted to.
spj.