It's not the parts, it's the skill of the builder. A 36-spoke 26" wheel on a 3-speed hub will be strong enough to carry several people if it's built and tensioned correctly. A good wheelbuilder can make crappy parts last forever. A poor wheelbuilder can take great parts and create a crappy wheel. Sometimes it's tough to tell the difference.

That being said- if you're carrying a bunch of weight on the back of that longtail, I would choose a wider rim, such as an Alex DX32: http://www.universalcycles.com/shopp...&category=1705 just to give the wheel some additional lateral stability.