I wouldn't tow anything with a minivan; they're too light duty. You'll want a long wheelbase for stability, extra large brakes to stop both vehicles and a heavy enough tow vehicle that the tow doesn't push it around. U-Haul won't rent a car trailer or dolly to you unless you have a 3/4 ton truck at a minimum. I towed a Spider on a trailer with one and I definitely felt it pushing the back of the truck around.
If you want to tow with an RV I would recommend at least a tow dolly, but a car trailer would be a better bet. Depending on how often you plan to use it buying one might be more cost effective than renting, though you might want to rent on your first trip to find out if towing is a PITA for you.
Tow bars can be hazardous when the towed vehicle's front wheels start steering out of phase with the tow vehicle. The more you try to correct, the more the towed vehicle wags the dog until both vehicles are off the road, along with any other cars you manage to collect in the process. Also there's really nowhere on a Spider to mount one; I read once where someone tried mounting one on the bumper and found all but two bumper mounting bolts snapped off when he got to his destination.
Why not just drive it? I drove a Spider from Pennsylvania to California along I-80 and even got to drive it on the Bonneville Salt Flats along the way (that was a mistake). It was quite an adventure.