Cal, I haven't done this either, but some people suggest doing it annually if you want to MAKE SURE you never have a reason for roadside assistance.
Part numbers are here:
http://www.epicmarine.com/docs/Trailer%20Maintenance.pdfYou could always call Ameritrail at (407) 892-1100 if you need advice.
This is also where you would buy brake pads if you needed to do them.
Not sure about whether bearing change involves brakes, but would imagine that you'd need to pull the calipers off (two bolts and then spread the pads) to get the rotors off to get the hubs off to change the bearings.
Sure it's not a SUPER simple thing, but $400 is a lot of ducks. When I do it, I'll probably combine with a brake fluid change/bleed. Need to do this ASAP since the fluid in there's like five years old.
I'd like to add a question to the group: how will Bearing Buddies work on our hubs? I'm not sure if the existing zirk has got to be removed, or if the bearing seals need to be replaced or what. I'm not very good about adding grease after EVERY trip to the water, and think the Buddies would help. Ameritrail was like, "all the different grease systems are basically the same." I had probably asked them something lame like, "why didn't you guys put Buddies on there?"