We now have our new Host Rainier TC as of Friday 12/2/16. We traded our HH 5th wheel for this TC and used it for the two nights on our way home from Cleveland, WI. We were very happy with our deal...
Congrats. Your Rainier sure is a lot different than mine!
I would consider upgrading to 19.5s. I carried mine on a SRW for about 8 years. Keep in mind that you will increase the weight quite a lot by having a full holding tank and full fuel tanks.