Over the years I have built several scratch built trucks , farm related machines, construction and mining equipment models. I even built one Great Lakes freighter model.
I have always used 18 ga. sheet metal because it is easy to cut and very strong when tacked into place. My small 100 amp wire welder does a excellent job.
This is the largest static model I have built and it is my favorite . I just had to build the rear ripper assembly.
Attachment 5006