Good luck with that...
Almost NO ONE allows towing with rental vehicles, too much liability. Besides, you are talking about Semi-level stuff.
Try Ryder, but it might just be cheaper (and safer) in the end to hire a tow company. What are you trying to haul that requires 20K? Certainly not an RV.
You are the maximum for a hotshot load. You won’t be renting a truck and trailer. You should call a broker and arrange for a hot shot load Pt A to Pt B. You pay for driver, rig and broker. Better be accurate on the weight as you could easily be hiring a flatbed or dry van.
Drivers are hungry right now. You might get a pretty good deal.