Good topic
I've wanted to do this for years. I think this is a California only deal but, A cube van is not a trailer therefore the speed limit on the highway is 70 instead of 55 and they can drive in the fast lane. The biggest hitch seems to be size. I like to have some room to store stuff a 20' box would be good, most Ryder/U-haul trucks are 15'
I've thought of getting one built, compared to buying an enclosed trailer and a dedicated truck, it would probably be cost effective.

The other minor problem is, if you stay in a hotel you either need to drive the whole thing back to the hotel, or hitch a ride with someone.