If you are carrying a scooter on the back of a 5er, you'll definitely unload the pin by a similar (give or take) amount. There are toyhauler type 5ers that might suit you but I'm not aware of any that weigh in under 12,900 GVWR. The problem presents itself that you still have that weight on your trailer thus reducing your other cargo carrying ability. 12,900lb is not a lot of 5er trailer but if you are comfortable in such small/lighter rigs then have at it. Don't forget you still need to add the weight of 5er hitch in the bed of your truck, add fuel, passengers any other cargo you carry in the truck itself. So be wary of the claim that it will tow 12,900 lbs. You may run out of rear axle capacity in the truck long before you reach 12,900 lbs of trailer weight. 20-25% of your trailer weight will be riding on the hitch in the truck. Putting a scooter and associated mounting/support hardware on the back of the 5er will push that number down closer to 20% or possibly less. It's all a rather tricky balancing act, axle ratings, pin weights, cargo capacity, combined vehicle weight ratings, so know and understand what they mean as they apply to your situation. There several calculators out there to help you figure what you can and cannot do safely. A starting point is reading the data off the sticker on your truck regarding axle ratings, etc. Then get the data on pin weights, trailer axle ratings, GVWR (Gross vehicle weight rating) cargo carrying capacity (and know what that includes as each mfr seems to use different criteria to assert their claims.)

FWIW, Brian

We have a 36' Mobile Suite and tow/haul 2 Vespa scooters on a swivel wheel trailer.    Attaches to the hitch on the back of the fifth wheel and has a single swivel wheel.    Capacity is 1000 pounds, weight on hitch is designed at 400 pounds, and  our scooters weigh aprox 500 lbs.    we have had for 1 year with no issues or problems.    Let me know if you have any questions