Of course the winds to worry about are the ones hitting your RV from the side. Driving facing into, or along with, winds should be of no concern if you feel that you can always depend upon facing into or driving along with them - which to me would be taking a chance ... for instance, how about curves in the highway which could temporarily cause the winds to hit you from the sides?
However with guaranteed side-winds I'd stay out of winds with speeds over about 30 MPH towing anything, whether it be TT or 5'er. I've never owned a TT or 5'er, but I am a cautious enough person to not risk it just based on estimating the physics of what could happen when towing. A 5'er definitely seems safer to tow than a TT under any conditions.
Just as a data point, we do have a short motorhome on a wide stance (E450 ton and a half series) chassis with side-by-side rear duals and only 11 feet 3 inches of height, so lateral (side-to-side) stability is quite good. We have driven on the high desert open highway in New Mexico with 60-70 MPH wind gusts coming at us from the sides. It took all my attention to do it and we did slow up to around 50 MPH speed, but it was doable. I'd NEVER have tried this towing anything, however.