Just about nobody is going to rent a tow dolly and let you hook it to a 1/2 ton truck for liabilty reasons. You will have to tell them you are towing a VW with no engine or something to rent it. Most places will require at least a 3/4 ton truck with an upgraded hitch to rent a tow dolly. If they rent to you and your hitch doesn't hold up or the wieght pushes you and causes a wreck they can get sued for big $$$$.
I have a 71 chevy 1/2 ton truck that wieghs in at 5000lbs, and with my Nova behind it wieghing 3600lbs, i need close to 1/4 mile between me and anyone in front of me to get stopped, and that is towing it on a trailer with trailer brakes.