My understanding of the front and center mounts is that they don't go thru the wood, but just into a plate on the bottom of the cross-sill with a lock washer, castle nut and cotter pin on top of that plate, but below the top of the cross-sill and the wood.
Yes - this is my understanding too. I have the carriage bolts when ordering a kit, but I also bought some hex bolts if I'm going from the bottom side. Guess I'll decide when the time comes.
