I'm halfway to making a circular saw sled inspired by @Bill Fitzmaurice's sled as outlined in his subwoofer plans - I've screwed a length of batten the same length as the width of the ply sheet to the end of the ply sheet. Next stage, when I've got a decent blade for my (t)rusty Black & Decker [1][2], is to cut across the sheet with the batten as a guide, and then all I have to do is put the edge of the sled along the line I want to cut and it will cut along it. That's the plan, anyway.
 
	 
 
	[1] Whose sister Carol did such a magnificent job of singing for T'Pau
 
	[2] That should double its value