Buckled tandem wheel + trailer?

Unfortunately for you, the Bob Yack trailer, when loaded, has a load bias toward the rear wheel of the bicycle to which it is attached. Not good for the bike!

Two suggestions:

1) Ditch the single wheeler in favour of a twin wheeler, where the load is biased to the trailer.

2) Get a wheelshop to spoke up a forty spoke rear wheel with with a triple cross pattern for extra strength and durability..

And try not to overload the trailer!

Most buy cheap drugs of the buckling occurs during acceleration/braking, when there is a phenomenal amount of torque being loaded and dissipated through a wheel and with modern eight and nine speed cassette type gearing with very shallow dishing, the problems are greatly exacerbated. You could specify a wheel with no more than six or seven gears and still have a good enough spread of ratios for all but the toughest and steepest of circumstances. In fact, fewer gears, with wider spread ratios are far more suited to towing.