[rhagfo]

So being from the PNW, found this question interesting until I saw your location.
Towing in the rain you just need to use a bit more caution, how long since it has rained in the area?? If it has been quite a while oil build up on the road will make it just a bit more slippery.
Watch your tire pressure!! Many state Max side wall always, so wrong for wet conditions, inflate based on an load/inflation chart. example, my rear axle tires are rated at 3,415# ea, @ 80 psi, load on the axles is about 5,500# so I run them at 65 to 70 psi, keeps more tread in contact with the road. The same is true for my 5er, less than 10,000# on tires rated for 12,168# as they are also LT truck tires run them at 70 psi also.