We tow a BOB behind our tandem and it has worked great. It comes with a heavy yellow dry-bag - for our latest tour we used two Sea to Summit duffle bags which each weigh 3 ounces. That saved 3 pounds.
Word of caution - One one trip my wife briefly towed the BOB behind her single and on a descent in Vermont it started fishtailing, something that never happens behind the tandem - the tandem is too long and our combined weight is too much for the trailer to push the bike around. Way back I towed our kids in a Burley behind a single mountain bike down Cadillac Mountain at Acadia and had no problem. I don't know that there is a way to prevent a single wheel trailer from doing that as the trailer does not have brakes.