Okay, a complete picture (wrong word; I have no image of the setup, so this will be a mental picture) of my California-legal, single axle, braked trailer's coupleing system:
Tow vehicle (Toyota 4-Runner, 2003 model) has a built-in trailer hitch. The hitch is (I think) a bolt-on affair, the business part of which is a square receiver tube, with a 1/4" steel "loops" below and to either side of the receiver.
Trailer has an Attwood hydraulic surge brake coupler, with a built-in breakaway cable for brake activation in case of separation. (see http://shop.easternmarine.com/index....categoryID=150
Attached to the trailer tonge are 2 chains, about 2.5 feet long or so, with J hooks at the ends.
Connection is straightforward: Couple the coupler, cross chains under tongue, attach one J hook to each of the steel eyes, and connect the breakaway cable to one of the eyes.
If the trailer comes loose (ball fails, coupler fails, receiver pin fails and receiver comes out of tube), two things happen: The trailer tongue falls onto the chains, which cradle it in the "X" formed by crossing the chains. While the tongue falls, the breakaway cable is pulled from the coupler, applying the brakes.
Result is that the trailer remains attached to the truck, trailer brakes are applied which means the trailer won't overtake the vehicle (unless vehicle brakes are applied more aggressively than the trailer brakes will slow the trailer), and everything remains sort of under control.
On the forced uncoupling issue, have heard from several people who trailer to ramps with an abrupt transition from flat to slope that the problem exists. Usually, it occurs with multi-axle trailers (and hence, heavy boats.) As the center of the wheel arrangement drops onto the ramp, the trailer tries to re-equalize the weight on the trailer wheels, which translates into levering the tongue skyward, and the tongue ends up pulling up on the coupler with quite a bit of force. If you've ever looked the actual coupling part of the coupler, it probably won't surprise you that it is a fairly weak spot in the system.
A single axle trailer should not have this problem, as there won't be any equalizing to be done, so no force on the coupler, as long as the max angular offset between the ball and coupler are not exceeded (which would, I believe, make for a *really* steep ramp.)
Sorry for the overly long post;