If you live in a decent area, in my opinion you needn't worry about having your van broken into if it's obviously signed as a carpet cleaner's vehicle.
I live on a housing estate on the edge of my town, it's granny-ville mostly with some little areas of executive housing and plenty of 50s and 60s couples.
My next-door neighbour is a plumber. He's had his van broken in to, or attempts made to do so, probably once every 6 months or so. 10 yards away sits my van, untouched..... I sometimes forget to lock it at night!!!
Scumbags only want to nick kit that they can easily and quickly sell down the pub the next night, that's the way I reason it. Drills, saws etc etc..
As for the frost thing, that's another entirely different matter. You NEED to protect your kit and products from the cold. I remove my machine, solution lines, wand/hand tools, sprayers and susceptible bottles of solution from the van overnight and store them in the garage with a heater set to keep the air temperature to around 5 degrees.
Along with the other kit and products in storage there, I'd probably be looking at one month's profit to replace or repair everything perishable by the cold if I didn't heat it. Well worth the pound or so per day it costs to protect it
