I had a cheap nanny cam that I used to check on my son after he got home from school. I could see him sitting on the couch on my phone while at work. It could even pan around the room a little bit. Was like $30.

That was at my house. But I don't see why it wouldn't work in a van with a hotspot just as well. Just required USB power and wifi.

They also have temperature gauges which work over wifi. Would be nice to find something that has them both integrated together. Perhaps there is some 'smart home' solution that would work. Again, as long as you have USB power and wifi network connection, it shouldn't matter whether its a house or van.

https://www.amazon.com/WUUK-Security-Detection-Tracking-Compatible/dp/B0B7MKSLT6

https://www.amazon.com/Smart-WiFi-Temperature-Humidity-Monitor/dp/B08YRKLHLD

EDIT: A bit pricier, but this seems to do both. Can do sound and motion alerts, etc. Pretty neat. Looks like they are marketing it for use in RV's.

https://www.amazon.com/EGLOO-Security-Temperature-Humidity-Appliance/dp/B0972PX5NF