I have built 2 kayak trailers based on the 40" x 48" Mini utility trailer kit from Harbor frieght and heard of several others doing the same. Last week I burned out a bearing set and tried to get replacement parts. A rebuild kit (bearings, seal, cotter, and dustcap) for the basic 1" x 2" set is around $10.00 and readily available. The mini trailer kit uses 25mm x 52mm. I was able to find bearings and seals locally but they wanted more than $30.00. I Couldn't find a dust cap in the right size except for a set of "Bearing Buddy" caps shipped direct from BB for another $30.00. Harbor freight can't get parts for at least 2 weeks and it looks like they would be at least $50.00 plus shipping.
Suddenly my $160.00 trailer kit Isn't so inexspensive anymore.

For $75.00 at the local trailer supply shop I bought all the parts I need to convert to the 1" spindle set including bearing buddies. If I burn another set I can get parts at most farm or marine stores.

P.S. I noticed my owners manual calls for removing and repacking the bearings at least once a year - now I know why.