Can you really call it planking when you whack on great plywood panels ?
Regardless, the planking has started. Cutting a 4'x8' sheet of ply* into 2 2'x8' sheets is not trivial unless you happen to have a panel saw.
To do it on a table saw, you really need extended rollers to allow you to control it. A typical circular saw is a little big and heavy for cutting 6mm ply.
So..... More Tools!!
I got an 18v trim saw. This one was a cheapo special, against my better judgement, but I reasoned that I'd only need to cut a few sheets, and I may never use it again. When will I learn ? The Battery won't hold a charge overnight, but freshly charged it's not bad.
To avoid massive breakout on the ply, I make the first cut about 3mm deep, half way through the plywood. This means the blade is exiting the wood moving forward rather than up. The plywood is supported by the wood in front of it, no breakout. Then I follow the same cut with the blade just through the wood. This is easier that you might think. The saw is small and easy to control with one hand.
The result, at the cost of a little extra work, is a nice clean cut.
So I now have the first two panels clamped into place on the frame. The fit looks really good. Of course these are the aft panels. It's the fit at the pointy end that's difficult.
(*2440mm X 1220mm doesn't metric make things easier?)