Hi, with standard taper roller bearings, stripping them down, cleaning and re-packing with grease is the norm, I'm afraid! Still, I'm not complaining, it keeps my kids fed
If you were of the persuasion then you could drill and tap the rear of the drum and fit a grease nipple (I've done it for a few people with unbraked trailers), but tbh, I'm not convinced there's any great gain. You still have to whip the wheel off and try and line the grease gun up, which can be a bit of a pita if the boats on it. Just as quick to strip it down and re-grease it IMO. Not only that, it gives you the opportunity to inspect the bearings at the same time. No point pumping grease in to a set of bearings that have rusted and are in their way it anyway
Bearing buddies / savers are great, more so if they're the spring assisted type, as these keep a continual pressure on the grease, pushing it in to the bearings when needed. The non-sprung ones are a bit like having a grease cap full of grease really. However, there's plenty of people on here who run both types, so you're bound to get feedback on both types.
If you measure the inside of your drum boss (where the dust cap pushes in) then you should be able to source a pair fairly readily from the web. Try Trailertek for starters, they've a pretty good selection.
All the best.