@skierdude The length is probably an insurmountable issue. The comment about making the trailer higher off the ground to flow more air under it would make matters far worse. Not only would it raise the trailer's center of gravity making it less stable all by itself, it would increase air turbulence increasing lift and also serve to increase the sail area making the trailer more reactive to cross-wind. If anything you want to effectively reduce the height of the trailer. Just look at all the semi trailers with skirts along the sides. They can't lower the height of the trailer so they do the next best thing, they reduced the turbulence underneath. I've never seen a TT with skirts but you get the idea.
You've already gotten good advice in this thread regarding weight and balance as well as WDH and stabilizers.
Everything else you can try is going to be an expensive experiment. The stock tires on the trailer might not be the best quality, you can try upgrading them with an eye to the stiffest sidewalls you can find. Same for the Ascent. I'm not actually telling you to do this, because I doubt that it will be a cure. Just trying to give you an idea that fixing physics is going to be trial and error and there are costs and risks to be considered.
You've already gotten good advice in this thread regarding weight and balance as well as WDH and stabilizers.
Everything else you can try is going to be an expensive experiment. The stock tires on the trailer might not be the best quality, you can try upgrading them with an eye to the stiffest sidewalls you can find. Same for the Ascent. I'm not actually telling you to do this, because I doubt that it will be a cure. Just trying to give you an idea that fixing physics is going to be trial and error and there are costs and risks to be considered.