Those portable AC units aren't that small. Have you considered a small trailer (popup, travel trailer or teardrop)?
Yeah, 30" tall by 13-14" wide, 50 lbs. In a conversion van there would be space between the front and the conversion bed. This is where I put my dog crates and some of the equipment (
link). Then there is space in the back for quite a bit of stuff, but for the bed to be flat stuff needs to be moved. We took the third bench facing backwards out first so the bed was a double, not a queen.
But I am sure every conversion van is different.