Find your electrical panel and hopefully one of the breakers is labeled as being for the air conditioner. My guess is that it will be a 15amp breaker. There is a small chance that the van manufacturer wired that circuit for 20amps and put in a 20amp breaker but you'll probably find it is 15amps.
110v and 15amps will narrow down your choices for a window type air conditioner.
I found 3 here.
There are so many 220/240v units out there now.