El Camino Man, your 2003 Salem 25RLSS @ under 7,000 dry is already one of the smaller, lighter 5ers, so I can't see how much MPG you would save by going a tad smaller. Also, the resale value on a 2003 isn't all that great, so I don't see how you would save by trading it in for something else, especially a newer Scamp...
IMO you would be better-off keeping your Salem & trading-in your 1996 F250 Powerstroke Diesel for a F150 Ecoboost w/HD package. The EB gets better mileage, especially when not towing, and uses gas vs. diesel. In our area, 30 gallons of gas is $56 compared to $100+ for diesel... However, due to the hitch weight of a 5er, you would have to get the HD package...
2011 RAM 2500 ST Crew Cab 5.7 Hemi
2011 Primetime 3150BHD Touring Edition
Days camped in 2016-36
Days camped in 2015-37
; Days camped in 2014-31