We're considering towing an Xmax on a Navion 24D, which has a 500lb vertical tongue weight limit.
Since the Xmax weighs 397 lbs, that rules out a Hitch Carrier, so we're considering a towing trailer instead... Something like a Kendon "Go! Series Single Rail Folding Motorcycle Trailer".
Please chime in with your recommendations and experience with a relatively heavy scooter (that sits 2).
The problem is that you don't really have 500 lbs to work with!
Basically,
The effective tongue weight limit decreases as you move away from the hitch.
(E.g., In your case, the carrier is 1 to 2 ft away from the hitch)
Here's an example of what you can expect when using a Hitch Carrier: Boss Truck Accessories
(scroll down to How to determine weight capacity)