I have about 1500 miles on mine since March and they seem to be holding up fine. I will likely change them out in the Spring before we do our big trip. But for the shorty trips we have been doing (all under 300 miles) I have not worried about them. Keep them aired up to max PSI, keep the speed at or below 65 and protect them from the sun when in storage and they should last a good while.
As for replacements, I will be going to the Maxxis M8008 ST tire. I have had them on two previous trailers and they were great. If I had 16" rims, I might consider going to an LT tire.
Current TV:'14 F350 Lariat CrewCab, 4x4 Short Bed SRW Diesel w/ Pullrite 2700 (16K)
Current Fiver: '15 Puma 295BHSS Anniversary Edition
Past TV: '13 F150 HD Payload SCrew EB, '08 Tundra CrewMax 5.7L, '02 'Burb 5.3L, '97 Dakota 3.9L
Past Trailers: '09 Wildwood LE 27RB, '02 Palomino Yearling RL, '87 Jayco 1006dlx