Technically, rear axle and trailer should have chains if it is that bad.
Depending on the chains and tensioners, 20mph is totally doable.
I have been in the mountain passes in Oregon when chains were required on every vehicle (conditional closure) a handful of times. I ran them on the rear of the Ranger a couple of times, and on all four on my old 4x4 VW van. But basically, using them sucks. If I was in a spot where I had to use them to get around, I probably wouldn't bother towing unless I was on some cross country move and was going to be stranded somewhere.
2006 F150 FX4 Super Crew - Bilstien 5100s leveled 2", 35" KM2s, 4.56 gears, Detroit locker, Eaton E-Locker, Traction Bars, AEM intake, Xcal 2
2010 VW Golf TDI 6MT