I bought these tire from tire rack. If you look on the tire rack site, they have local tire shops that have an agreement with them to do the mounting. The mounting charges will vary. I took the wheels off one side of the trailer at home, took them to the shop, had the mount and balance done, brought them home and remounted the wheels, then did the other side. I also had the valve stems replaced with the correct metal snap in stems. Don't forget to have them balanced ( IMO ).
EDIT: also, don't forget to retorque the wheels after 20 miles or so, and a again at 50 to 75 miles, then a final check after 100 to 150 miles. Or whatever it specified on the sticker on your trailer.