Yes I carry spare bearings, I rarely pull and re pack trailers. Keep grease in them and you don't need to repack regualrly at all. Just like old cars, maybe re pack every 30k or so.
Easy lubes are easy to not blow seals. Pop the caps off before greasing.
Don't be paranoid that the trailer came with mythically bad grease, but do make sure the hubs are full.
You haven't had issues because nothing is wrong. Just make sure there's sufficient grease in them.
I've only blown bearings that got the snot run out of them, like 12" wheels on a snowmachine trailer running long distances at high speed. One of those little tires at 80 mph is doing about a buck thirty!
At 3000miles on such a lightly loaded trailer I wouldn't be worried about re packing them.