You should ask him but I believe he's publicly stated it's intended for a few hundred pounds, bicycles kayaks etc.
The problem isn't making a hitch strong enough, easy to do with welded steel. The problem is finding a strong enough place to attach it. There is no frame to speak of in the back of an Insight, just formed aluminum sheet. Which, for the most part, you could seriously damage with your bare hands nevermind the forces of an 800 pound trailer under heavy braking or bouncing over uneven pavement. The hitch designs posted on here, like Scott's, try to alleviate that by attaching at multiple places to spread out the load. But the places they attach are all inherently weak and I don't think anyone has done any real engineering or testing to failure so the real capacity is just a SWAG.
I have two trailers I tow. Both are designed for motorcycles or small cars. One is a cargo trailer and the other is a pop up tent trailer.
The cargo trailer is about 150lbs empty. I think loaded I’ve been about 500lbs. I’ve carried tools, transmission, springs, parts, etc.
The tent trailer is about 325lbs empty. Loaded I think it’s been about 600lbs. It has cargo space for camp gear.
Unibody cars still have what is considered a frame. My hitch design bolts through the rear frame rails. It does require drilling. There are no existing holes to use. My design is two pieces. One part goes inside the trunk area and bolts through the frame rails and then there is another piece that goes on the out side of the rear body panel, the two pieces are basically angle iron, that bolt back to back making a very strong beam. The outer piece also has a bracket that bolts around the rear bumper reinforcement to add more stability, or spread the load, as ackattacker stated above.
The receiver on my hitch is 1 1/4x1 1/4, it is mounted up high hidden under the license plate. The brace on my hitch that goes to the bumper reinforcement transfers some of the load against the the reinforcement pushing it tighter against the frame rails.
The rear bumper reinforcement is not strong for pulling at all. It is only held to the rear body panel by four bolts that are only spot welded to the rear panel. The bumper reinforcement is really only designed for an impact, in which case it get pushed tighter to the frame rails.
Towing an 800lbs load is probably excessive. I’m not saying it won’t do it, but it’s probably unsafe.
We own a tow truck at our shop. I’ve towed a number of Insights. One problem I’ve encountered is the Insights park break doesn’t hold very well on the slope of the tow truck bed. I can’t imagine putting 800lbs of load pulling backwards toward a body of water. If you were able to not launch the car, once you were loaded back up with 800lbs on a slope the car might have a very difficult time climbing back up the slope, wet or not.
