I don't think you'll find any OE 18ga on the truck, other than floor and formed stiffeners, and the repro panels available for the TF series now are the correct 20 and 22ga where appropriate ... I recall there being 6 bed mount bolts on a short box

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics