Had the same problem, we fabricated an insert that fits inside the hitch brace - the round one - and bent a bracket that runs under the edge of the bumper and up beside it so the 'button' fits right on it. Very solid, although it took us a couple hours with a torch and welder ... but we designed and fabricated as we went - so, might take less once you see the finished product.
Had talked to Happi-jac earlier and they sent the 'preliminary' drawing for the button plate, but with the 'plastic bumper' section right there, I personally decided it wasn't as safe as I want ...
Never posted a photo on here - don't even know how - but if you want a photo, send me a PM with your email and I'll email one to you ..
