Man that Moby Dick cracking after 2 months stings, all that work down the drain. Been there with a cheap glue-up on a Thrift Store find and it split right at the hinge the first cold week. 1mm goatskin sounds about right to me for a heavy book, I've gone down to 0.8mm on smaller stuff and it still holds. Anything thinner than that and you're basically just gluing paper to the boards.

Graphite is a dry lube so it won't grab grit, but silicone spray is actually a wet lube and that's why it cakes up with sand at Port Angeles. Just know graphite can stain light colored seals and fabric over time.

My uncle hauled a old 580 Case back in the 90s and swore the same thing your dad did, four corners through the tracks or it dont move. Then one day he watched a kid with a brand new setup run one strap over the bucket and it sat fine all the way to Salina. Thing was that kid had a set of those rubber track pads and a deck with a lip welded on the back, so the machine couldnt slide even if it wanted to. My uncle still ran four points after that, mainly cause he didnt trust new stuff, but I never forgot that the deck itself did half the work.