Low Oil Pressure

I'd guess a switch or sending unit.  A precautionary tale; on a different make and model, we recently experienced a similar intermittent oil pressure drop (to zero) without much rhyme or reason.  Turns out the oil pump's gear had been slipping on the shaft connected to the gerotor.  After sufficient heat buildup, it would grab on again. 

As you are only seeing your issue during towing, oil or engine temperature could be a factor.  Definitely best to figure out what your issue(s) is/are quickly before any nasty surprises.  Good luck!