Bearings are easy to replace. Do it yourself. I wouldn't trust Pep Boys to have the parts or the know how to do it right.
You can find the military technical manual for the M416 in .pdf format free on the Internet. (See the link Scott posted - it is one of the most comprehensive on the M416 http://vegasauto.net/m416.html) There are step by step instructions in the manual. Also, if you search the Yahoo M416 group and the 1/4 ton trailer forum at www.g503.com, you can find a complete parts list for bearing replacement (see links at http://vegasauto.net/m416.html.) Parts are readily available from numerous sources.
You can run tubeless tires on your stock M416 trailer wheels or stick with military NDCC tires and tubes. The advantage to tubeless is that you can match the size/style to your tow rig and use a Safety Seal tire repair kit if you have tire trouble. With a tube, you need to remove, patch and replace. (That being said, I have military tube type tires on my Bantam trailer and have never had a problem. If I do, I know how to break the bead with tire "spoons" and replace the tube in the field.)
Shasta County, California
'05 Nissan Xterra Off Road
'46 Bantam T3-C trailer