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.
When i purchased my 88 Spider, I towed her on a tow dolly behind my chev s10 v6 4x4 about 250 miles home on mostly interstate hwy. If you use a dolly, you will have to put the front wheels on the dolly to keep from having the aforementioned tail wagging danerous situation ocur. If you do this, you really need to disconnect the driveshaft as well from the final drive pinion flange which is a PITA for just a short trip.
The s10 4x4 had enough weight and stability to handle the spider and the 4.3v6 had plenty of power but i wouldn't want to tow with anything lighter like a minivan or whatever. The full trailer would be better but you also have to consider the extra weight of the trailer when determining max towing load for the tow vehicle. best of luck
There is no structure built into the Spider that enables towing (as you described) by another vehicle using a tow bar. And if the rear wheels are going to be on the ground for anything but a very short distance you have to add more diff oil. (Your Owners Manual has instructions on this.) The only choice is to have it trailered or towed with a vehicle built for towing.
I've owned varioius Spiders over the past 15 years and towed each of them four-down many times. Two different cars went back and forth from central NJ to northern Virginia using my mini-van.
I made the tow bar for an MGA I had for many years and modified it to fit the front bumper mounts on the Alfa. Made sure it wasn't in gear and with the ones which needed work, I pulled off the calipers before hitting the road since I was going to be rebuilding them anyway.
Drove on I-95 both long trips at 65 with no problems at all. Naturally, was careful not to make any sudden turns and kept watching the mirrors the entire time.
Thought about disconnecting the drive shaft but never got around to it.
It worked for me but you obviously make your own decison about what is safe and what is not.
I towed my Alpha Romeo Veloce from Ft Lauderdale, FL to McLean, VA using a UHAUL dolley on a Toyota Sienna van without a problem two years ago. I did 65 MPH most of the way on I-95. Stopped regularly to check the hitch and tie down belt straps. I disconnected the drive shaft a the rear and tied it up with a two coat hangers.