[goodellj]

Lots of comments about how "any one can do this" and "it's easy". Bottom line is that it MUST be done periodically and 5 years is WAY too long,. If you just aren't comfortable doing it or would rather leave it a professional, so be it. This is one of the required maintenance items, like winterization.
I burned out a bearing once and you don't want this to happen to you. I now pay extra attention to periodic wheel maintenance. (I've had similar experience with E-rated tires. Nuff said about that).
I put about 6,000 miles a year on my trailer. I have a professional grease the bearing every 2 years. I remove the rubber cap and give each wheel a few pumps of grease through the zirk fitting before every big trip (remember that the wheel must be spun while doing this). We stop at rest stops every 100 miles or so, and I walk around with a Non-contact Digital Laser Infrared Thermometer Temperature Gun and take the temps of all the tires, rims, brakes, and hubs.