At a refresher course last weekend, both John Carmody and Todd Wright (instructors) had added short climbing "quickdraws" to their rescue 'biners. In climbing, quickdraws are used between two carabiners to reduce the angle of pull during a fall, so even though they're webbing, they're rated to several hundred pounds. The benefit seemed to be to separate the knot from the 'biner end and decrease the probability of jamming under the deck lines. They're cheap (3-5$) and come in different lenghts (4", 6" and 11"). I've added them to my tow system, but haven't tested them yet.
Phil