So take 100# off, but seriously being that, it probably added 2-300# in extra support. Like cars, a convertible always weights more than a sedan.

 

Yeah, I forgot about the double wall frame. That will easily increase the weight 1,000 pounds.

 

yes, but that's more for uni-body, this thing sits on frame rails like railroad tracks, I doubt they had to reinforce after reducing the cab

 

All F7's F8's had double-wall frames. I think Joe's 12k - 13k may be high, but not likely much. Those fire bodies are usually very stout steel. The cab is the same as an F1's, three men can easily lift one. Leaving off the doors and roof isn't reducing much weight.