I try use rotors pistons and landing gears to make separate grids. The last and biggest tower is separate grid. I will make screenshot to show this. You cant see gap betwen them if you dont know where is hidden. All grids have separate physic number of shapes. Minus of this is all engines and the Bridge mast be on the same grid but nod a power units like battery or reactors

Wow good luck, I built a 1600m Imperial star Destroyer and it destabilized the game physics at only 70% complete

Looks big an a lot of work done already