Do you have good, working dash AC?
If so, a remote thermometer and a remote starter might be worth looking into. If you park close to your workspace, an inexpensive "indoor/outdoor" thermometer would let you keep tabs on the van temp and you could use your remote starter to fire it up and run the ac as needed.
I recently bought a remote start/security system for my Grand Caravan that has a two way remote with a one mile range and hot/cold auto start feature. I can check the van temp with the push of a button, or set it to automatically start the vehicle at preset temps. It was kinda pricey and I haven't had a chance to really put it to the test yet.
https://www.compustar.com/product/prime-9000/
A remote thermometer and a simple remote starter should work just as well at shorter distances.
