they are old, and not "up armored" they are pretty bare bones. i think the turret makes more aerodymanic drag than the weight of the truck.
they only weigh ~6k each,
one was on a two car trailer by itself
one hooked to my truck is on a normal (3500# axles) trailer. it has a steel deck, so it holds up better than wood. but it's really too much weight for that trailer.
most newer deisel trucks tip ~7000#'s, and my 2006 CTD is a pathetic pooch, it's pretty slow.
i blew up my 2004 CTD twice, with a downloader.
long story, but I don't mod diesels much any more
i get 15~18mpg, so i don't worry about it.
i think i got 10~12 pulling the nova in the 24 ft enclosed trailer @ 70.