I balance every tire, trailer or not. The reduced wear and vibration are worth the small cost.
I took the trailer to Discount Tire. They jacked the whole trailer up. (4 jacks, one at each spring mount) and changed the tires. Quick and easy.
I recommend the Maxxis if you are not going to a LT tire. Stay away from all tires made in China. You can run LT tires with a highway tread just fine as long as they are rated to carry the weight you need.
2003 GMC Serria 2500HD - Lotsa Mods.