welcome to the forum!
You have chosen a topic guaranteed to ignite the usual firestorm of stale hate and repressed rage!
Better get ready, because this is a charged topic with MB diesel enthusiasts, there is an alternative fuel section of the diesel forum up above where all the arguing has been compartmentalized
Having said that, theres a place in oberlin OH that sells VO at the pump ive stopped at numerous times across country, The VO quality is good, and the sale is legal as far fuel tax is concerned, a novelty in the VO world. Full Circle Fuels, search for their website.
As far as the trailer, I usually have not noticed a major negative change in fuel economy when I tow, even with cargo on the roof and a fully loaded utility trailer, it did not drop that much unless I was crossing grades. Check your axles preemptively though, the alteration in normal ride height made quick work of my aging axle rubber, and I had to replace them both a few hundred miles later. If the rubber is cracked horribly already, a trailer tow might finish them off before the trip begins