I keep a bar and 2 25lb plates in the truck, some resistance bands, and a 50lb sandbag on a pack frame. I hardly ever use the bands or bar. I made a pull up bar and do dead hangs and pull ups, push ups, squats, and lunges. I'll put my pack on and do the same, and grab my 2 25lb plates and do step ups on my step box.
Back in the 80s I had a weight lifting machine set up between the seats of my autocar day cab. I ended up winning a WIL Volvo with a aftermarket double eagle sleeper in an arm wrestling competition.
I used to carry some plates, dumbbells and resistance bands in my headache rack. But over time I found bodyweight movements with a weighted vest worked better. It's not ideal by any means but it gets it done.
........you......you mean you haven't seen the ultimate workout plan while in and around the rig!!??? I paid 89.99 for it...but I'll share it with you for free.