I've come up with the answer for the entire rig that seems to suit us best. Fortunately the DW agrees with me as this would be the trip of a lifetime so budget isn't a great issue.
Truck- a 3/4 or 1 ton SRW probably king cab with either an older(pre 2007 diesel or gas) We would get a used flat bed for it and then put in air ride seats. Many of the non main roads are just a constant wash board we will have had by then 5 back operations and a couple of hips so some extra money for air ride seats is more a requirement than luxury. The flat bed is so we can carry things like macerator pumps and a small generator fairly easily.
Camper- Small size seems to count, The Trek of the Americas folks have bigger rigs, but seem to stay in the more developed areas, other folks like the hackneys and Kathy and Rick from travelin tortuga say to go as small as comfortable. So we would find higher end used popup, since we're in Colorado probably the aluminum framed Outfitter 9.5. For the rough roads wood frames seem to be too fragile. We started out with a wood frame Hallmark 12 years ago and loved it, but the wood frame did prove to be not sturdy enough on Mexican roads.
Toilet setup- A portable macerator pump and long hose. This eliminates having to modify a perfectly good camper, and I don't haul 6 gallon water jugs anymore.
Power-primarily solar with a 2kw inverter and and back up generator, we have 2kw Honda. People seem to have electrical hookups only a few times a trip, so independence is very important.
So next spring I'll probably start putting this rig together. I've got to get thru another back fusion first.