I've had a whole bunch of trailers and never balanced any of their tires. They aren't balanced as the trailer comes from the factory. Probably 95%+ of trailer owners never balance their tires.
Should they be balanced? It could only help with the ride inside the trailer (illegal in most states for most trailers), might be easier on the "stuff" riding in the trailer (most of the stuff we haul isn't vibration sensitive though), might make the tires last longer (most of us never wear the tires out, they have to be replaced due to age long before the tread wears off). So, from a purely technical standpoint, any revolving object will revolve better if balanced, but, from a practical standpoint, little is achieved. If I ever replace the tires, I'll have them balanced, but, to be honest, I've never kept an RV trailer long enough to have to replace the tires and my utility trailer is / was (I sold it last year) 17 years old and still riding on the original radial tires that it came with. As for balancing type, static is OK, but, IMHO, spin is the best. Beads? Great idea, but, difficult to get into the tire and a real mess if you need to buy a new tire or need to have one patched or have a blow out. They do work though and are an option to pulling the wheel to take to a tire dealer for spin balancing.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)