Personally I am rebuilding a 55 chevy flatbed truck (again). With a wagon train style canvas cover. Actually the cover is Kevlar scraps from a guy who makes the Kevlar covers for the Alaska pipeline. The ribs are carbon fiber scraps from the Dreamliner. I was going to go with diesel because of the incredible horse power you can get out of diesel. But now I am reconsidering propane as I have two 300 gallon propane tank already on sight. Plus I can always convert it to alcohol or gas, and propane allows me one fuel source for cooking, refrigeration, heat as well as driving.
The truck goes anywhere. Places modern 4X4 rigs dare not tread. Made of real steel with old school cattle guards it plows through trees like vine maples as if they were not there. It can take some serious abuse. Day to day it is a cool work truck, powerful hauler capable of carrying 1.5 ton loads and looks great pulling the Airstream with the bikes on the bed. Classic.
In a SHTF scenario or deep woods camping hunting/fishing trip all the living gear, canopy ribs, cots, generator, propane stove oven, refrigerator, gear is all in the camping shed. That can all be loaded and bolted in place in half an hour or so.
So IMHO a flatbed dually is the Ultimate Bug Out Rig. Older is cooler stronger and a 350 can be maintained repaired even rebuilt by even the most mechanically challenged like myself