We once towed our 29' TT from Spokane to Seattle on the I-90 (which is many miles of open grassland). The winds were gusting around 40+ mph and it felt like I was driving on marbles, even though I had slowed waay down. Pulled into a rest stop and a trucker told us that even the big semis pull over in those high winds. Eventually made it to the CG and a fellow camper who travels the I-90 often has seen FWs blown clear over.
Not worth the risk and you need to pull over. Doesn't matter what speed you're going, strong gusting side winds can push you over due to the area of sidewall of your TT. Winds often pick up during the daytime and die down in the evening due to thermal updrafts caused by sunshine. Could try planning on towing just in mornings, taking a break during the day, and then heading out again in the evening when the winds have died down.