bearings aint your problem...its seals! any Taper roller bearing whammed full of grease, with a decent seal and a bearing saver fitted should last almost indefinetley. as long as you can keep the grease in and sea out they are 100% reliable.
maybe worth changing your axles/stubs and hubs for conventional TRB's.
the rate your eating bearings should pay for itself in a season! the old axle will be sellable too, perfectly adequate for any trailer....other than a boat one
sealed for life bearings are awful! they aint sealed and life is short!