I think the trailer was not loaded properly (not enough tongue weight) or the trailer ride height was not level. If the van was a E250 it should be more than enough. I have hauled all kinds of stuff(Bobcats,tractors, WF's HT trailer with four 18HT's and a supercat 22 on it) with my F350,F250 single rear tire with bumper hitch and never had a problem if you load the trailer right.

Sorry about your accident and hope you get it all sorted out.