Going to replace some older tires on a 26' camper trailer, <5000LBs. Dual axel. Currently running 205/75-14 radials. Prices are all over the place 30 to 200 bucks. Do I need Radial or is bias OK? How many plys, 4 6 8? Any brands to avoid? Special place to get from on the internet? Should I just go to Wal Mart as they have places all over the US if I need help in the future?