Take your max leg press weight, and half it, thats the max weight that would ever be put through them. The weight of the truck is irrelevant, its how much force you can put through them.
I agree with this provided you have something fixed to the ground to help you pull (a ladder?)
If you're just relying on the grip of your shoes against the tarmac to pull it, you wouldn't be able to put much more force than your own weight through the straps.