Be aware of a few things:
Some companies that rent vans that size prohibit taking them over state lines, or will charge mileage if you do. Also, many regular private insurance policies do not cover them because the rollover risk is too high. They are very dangerous in the hands of the inexperienced, because they are top-heavy, and they also tend to understeer somewhat.
Most importantly from my POV for road trips, they ride like a sack of rocks because they have no suspension to speak of. No way would I voluntarily spend hours on the highway in one of those things if I had any alternative.