Good question, I don't yet. But I do with other vehicles. Lets divide the question into two parts- 1. The wear and tear on the suspension. 2. The van's body and attached items.
1. The rear suspension is just Dumb simple and except for premature wear of the shocks little should harm it or lossen up parts. They are torqued, use fasteners that avoid loosening and have bushings that should withstand this with ease. The front is a bit more of an unknown as it is the drive axel and has considerable complexity that has yet to be tested here in the US. Some vehicles seem to thrive even with extreme abuse but others (m '85 F150) have front suspension systems that suffer from anything more than routine abuse. I spend the winter near the MX border and we witness the abuse the Border Patrol put there vehicles to. Young men and Women given big SUV's and Trucks with built up suspensions are no match for our desert roads. Lots of repairs generally caused by high speed. I would say use common sense as far as speed goes. Some vibration and tramping is probably ok.
2. Your wonderful cabinets are at risk here too. The van's body/frame is welded and adhesive glued together and is a unitized (one piece) structure. I have noticed no flexing at all on my van in normal use. Rigid structures can withstand terrific abuse and remain structurally intact. The Border Patrol abuse does not seem to wrack the body of vehicles. I'd travel so as to preserve your interior attachments and not worry about the Van.
My own experience on these unbelievable roads suggests you cannot harm a vehicle as easily as you think. My 4 Runner and former Samurai withstood thousands of miles of moderate speed over stuff you will probably never see. I only broke a sway bar attachment on the Toyota due in part to its previous life in Vermont with lots of salt corrosion. The replacement has been fine. Oh and one exhaust pipe hanger! No big deal. GO.
