I also have a Snipe trailer with 'sealed bearings' - I have a complete axle set built up, which I swap out annually, and refit new bearings into the removed hubs. Bearings are < £20 per side if you buy them from a car spares store
I tow around 8-10000 miles a year, including ( for the last 3) a 2500m round trip to Italy >> and so far no issues. ( I too take the spare hubs on long journeys jic)
I do agree that part of the 'trick' is not to dunk hot bearings into the briny
...... of course, I have now tempted fate
Jeff