I had the same type of problems with the dogs getting tangled as Stubby. I found the
BatziBelt, which is a strap with clips on both ends that attached to the D-ring on the back of the seatbelt harness and to a shackle you thread onto the chest strap of the seatbelt. Since I've been using the Batzibelts in addition to the seatbelt harnesses, I've haven't had any tangling incidents. It gives the dog a little more freedom, but not too much. ;)
They also sell harnesses on the Batzi website, but I think they look kind of flimsy. I bought Easy Rider seatbelt harnesses for my dogs.