Your best bet might be to kludge together a solution that allows you to remotely activate your engine block heater, but doesn’t leave any evidence to thieving passers by that there’s something worth stealing on your truck.
As mentioned by another poster, what you want to look for is one of those portable battery jump packs, but that also has a 110 volt outlet built into it. Charge this up during the day, and leave it in the truck at night.
Combine in a block heater. If your van doesn’t have one already, get one installed.
Finally, buy a timer outlet plug in.
You know, one of those things that you plug into an outlet that turns on and off a light in your house at predetermined times that you set.
You plug in the timer into the battery pack, and plug the block heater into the timer, and set it to turn on about an hour or half an hour before you normally head to your truck. If you can keep everything under the hood of your truck, or in the passenger compartment of your truck, then you don’t have to worry about opportunist thieves walking away with your stuff.
BC.