Battens already cut to length and drilled.
My circular saw proved capable of cutting a triple layer sandwich (once I set the cut height right). I used a different cutting pattern as I was cutting a maximum of 610mm - first a cut across at 300mm, then a second and third at 376mm. After that, I stacked the three pieces and cut at 276mm twice, so a total of five cuts.
First, I made the sled - I'd glued and screwed a length of batten across the panel, and just cut across using that as a guide.
Then I clamped up for the first cut, and found that when I'd just nipped up the fixing bolt for the blade that my definition of nipped up and the instructions definition of nipped up are different. Once rectified, off we went. The first cut is the shallowest.
After that first cut, I was able to use the piece I'd just cut off to rest the other side of the circular saw base on.
Another cut the same and then I stacked the wood.
And at last got to the final cut.
I still have to cut out holes in the front and rear.