A blog reader asked me to provide some answers to the title question, and not knowing if this subject has ever been covered before, I decided to start my search at various ND Miata forums, and write an article for discussion. Since our platform is RWD, towing with the front wheels on a dolly, or with a tow bar and all four wheels on the ground (aka flat towed, or 4-down), is generally forbidden.
Since the 6-speed manual transmission in the ND has no synchronizer on the countershaft, unlike the previous generation 6-speed manual transmission (NC) which does have one, there is nothing on the rotating output shaft to slosh oil about, so there will not be sufficient lubrication of the internals, as the vehicle is being towed with the rear wheels on the ground, and premature failure would be inevitable.
I have however, seen some discussion that there is evidence that the NC 6-speed manual transmission did indeed, lubricate the internals while being flat-towed (or, alternatively, with the front wheels on a dolly), because of a synchronizer on the countershaft that is continuously rotating in the gear oil residing in the bottom of the transmission, throwing oil on the main shaft and tail bushing. As an example, healeyman discusses his flat tow setup here. He also has instructions for removing the steering wheel lock on a NC, as well as instructions for fitting a Roadmaster baseplate and brackets on a NC, and my guess is that the ND is very similar (at least regarding the steering wheel lock).
That is good news, since although the housings differ slightly to accommodate the respective engines, Fiat made the wise decision to use the tougher NC-era manual transmission internals in our 124 Spiders, so there is a good possibility (requires further research) that we might be able to “flat tow” the car with a tow bar, even though officially, Fiat maintains that this is NOT an accepted practice.
There is no chance of towing these vehicles with the rear wheels on the ground, if they have an automatic transmission, which leads to the next question:
How can these cars be towed?
One possibility is to pull the vehicle on a dolly, with the rear wheels on deck, and the steering wheel lock disabled.
Another option is an open or enclosed car-hauler trailer, which tend to be quite large, heavy and involve cumbersome ramps.
I was pleasantly surprised to discover that Futura makes a single-axle version of their lowering trailer, which seems to be custom-made for our light vehicles, since it has a 2,620 pound load capacity (see the first photo at the beginning of the article). The trailer can be operated (lowered/raised) via remote control, which is probably necessitated by the fact that you can’t open the car door while the trailer is in the lowered ramp position. A video on their website implies that, most RV parks will agree that, since no ramps are required, this particular trailer will usually fit in the allocated parking spot, and not be considered a third on-site vehicle, as long as you agree to park your car on it, when returning to your site.
Since it is less than 18′ long, you should be able to park the trailered car in your garage, and yet, retain the ability to drive on and off of it in-place!