I've tried to true wheels on the dropouts of a bike but never built one. All my wheelbuilds are stand builds.
While you can build a wheel on the bike I feel the ergonimics, speed and precision you get with a proper truing stand has so far more than made up for the expense of the stand. Especially when you have eight bikes to true or build wheels for. And there's going to be even more wheels added when the little demon graduates from the trailer to actual bikes.
I have a simple park stand that wasn't all that expensive when I bough it. Now however I'm considering on getting the Park Tool TS-4.2 and that's pretty expensive. But that'll true all the wheels.

Then again the most important tool of all is the tension meter, which I should really calibrate at some point.

Anyway. My point is that if wheel building isn't one's hobby, then it's not a bad idea to pay someone to build fatbike wheels instead of doing it yourself.