Depends on how many miles the trailer gets pulled in a years time. Mine averages 8k-10k per year so I pull the hubs every other year to see whats going on with the brakes and bearings.
Some trailer owners have said they pull around 1200-1500 miles per year. JMO but those types could run for several years before R&R inside the hubs.
I've put over a dozen new and used non rv trailers in service work. I always pulled the hubs before they hit the road. Glad I did as I've seen a bearing set in a hub with no grease....no grease seal.....several cut or torn seals and even one the outer race didn't match the bearings.....and of course the usual too little grease.