You get what you can afford providing It will do the job safely, I'm not a big fan of gassers but I been driving diesels since the late 80's and owned them since 92' and once you get use to the torque you won't go back plus I like having more truck then I need.
The truck you see in the pic is my daily driver and has been since I ordered it in 01' and 359,000 miles ago.
I get 16 to 17 mpg( 8900# empty) in the summer and 10.5 steady towing (21,500 gross) w/3.73 gears running in O/D (I have the 6-speed manual) but I don't drive above 68 mph much and It has a 120hp chip with a 4" turbo back exhaust.
I'm looking right now for a replacement but the cost is crazy, just a XLT SRW F-350 crew cab LB are around 50 to 55K hell the F-150's are not a deal either.
I would think long and hard before you buy a used Diesel more so on the newer ones then the old, the maintenance is not a big deal but It's very important it gets done on-time and with quality stuff (filters and oils) these newer fuel systems are very fussy and don't like anything but good clean fuel( I don't remember who said they drain the water separator each month but hears to you
, very smart) so not knowing who took care of that stuff before you would be very unsettling for me.
Just like the others have said,The pin weights are around 20% in the real world, mine is 2180# with the trailer weight around 11,500# and like you said I'm sure theres a lot of them running over weight and don't even realize it.
Good luck on what ever you decide and enjoy the 2016 camping season