My old pop up had a tounge weight around 100lbs and towed beautifully. What I liked about it was that I could hitch and unhitch the thing by myself. I had only to get the ball close to the trailer socket and I could pop the thing in place. Once the tongue weight exceeds 250lbs, it becomes a bit more difficult to get things lined up - especially if you are on uneven ground. I thought that putting some of the moto weight on the truck (rear carrier) and less on the trailer would keep the trailer in a manageable range. Also as the trailer gets longer, backing it up to manuever gets harder.
Also, it might be worth investigating a class 4 receiver to increase the weight limit.
'03 KTM 450EXC
"If you know what you're doing, then you aren't learning anything." - A. Lincoln