Upon Further Review : Tatest from the Oklahoma Green Country is on to something .
Within a 500 mile radius I found some real bargains in full size vans .
My observation is the real bargains were 2013 and 2012 models coming off lease because there was a much bigger supply . Say $ 22,000 gets you a 6.0 gm 3500 Express and you might get a 15 passenger for that , That model also has a 6 speed automatic and not a 4 speed .
The Ford E350 passenger vans were $ 1000 to 2000 less but were 5.4 V8 with the less efficient 4 speed auto .
Moving down to a 2010 van might save you $3000 but the drivetrain is not as good and the miles are higher .
Plus the gas mileage is better on the 2012 up .
For 5 people travelling continuosly I would consider one of those new/used 3500 vans .
One could also consider towing a 6 x 12 cargo trailer ( less wind resistance ) that had full width bunks installed .
The trailer could keep you out of the weather and still be light weight and aerodynamic . They are available in aluminum ( more money ) and steel .
I would keep the trailer mods to a minimum, mainly vents and a fantastic fan .