Students have done it, mostly grad students. Unlikely you could park on a campus parking lot overnight. You can always park in a Walmart overnight.
In some places it is really cold, in others it is really hot. My friend has done 2 conversion vans and they cost her about $40k doing almost all the work herself (with her brothers and son doing electrical and woodworking. She thinks it is the greatest thing in the world but I find it very claustrophobic just standing in it (never mind sleeping in it).
If you are in a snowy place, you may get snowed into the parking lot for a few days. If you need mechanical work on the van, that may take a few days and you’d have no where to sleep.