I put together a prototype GOAT with the panels that Spencer made for us. Here's my first reactions
The Good: Bolt up construction for the entire payload took less than an hour.
The panels fit well together assuming well manufactured corner brackets with 90 degree angles..
The No 10 Bolts are also a great fit. There's about .01" of wiggle room, which is a good thing.
The hull is a freaking tank. We could throw it down a flight of concrete stairs and nothing would move.
The McCorner Brackets from McMaster are indeed McCrud. They had to be made with large tolerances because there's even inconstancy between some of the brackets which exacerbates spacing of the panels (below). Once tightened, the brackets flatten which creates about a 1/8" gap between top/bottom and the side panels. Only good thing is that the gap is consistent along all the edges.
We will definitely have to spot weld hex nuts to some of the brackets. It can be just the lower brackets for two panels, but there's no way we will be able to put the last panel on without them or without finding someone with 10 cm arm circumference and tiny, strong fingers.
The GOATIf we can't find brackets that are made with tight tolerances then we can use the McCrapster brackets. Shaving them down isn't an option because of the amount of material that would have to be removed, but we could adjust the mount hole placements by 1/8" to compensate. Not all of the angles of the brackets are exactly 90 degrees which causes warping (see pic below) so we would have to adjust them with a little elbow grease. It'll be somewhat time consuming but doable. Plus we would have brackets very specific to this hull. Not ideal, but an option.