I have a 2005 19' Keystone tandem axle travel trailer and (yes I know) never serviced the axles. I pumped some grease into the zerks every few years, but haven't repacked the bearings or adjusted the ...
In PA there is an annual required safety inspection, while the drums are removed it is a simple job to do an adjustment after they are put back in place, no need for automatic adjusters if one does proper maintenance.