I always understood the "ideal" tongue weight for any trailer is around 125lbs.
I use to tow a 19ft. and later a much heavier 21ft. boat behind a 1974 intermediate sized car. I adjusted the tongue weight of both of those trailers to 125lbs, and they tracked just fine up to about 70mph. Only the 21 footer had tandem axels and "surge" brakes.
The longer tongue would help control the "wag" significantly. Trailer hitch hight, to keep the trailer level is a good point.