I take it you have already used the trick of using a piece of plywoo with a piece on top, to act as a straight edge, and the bottom piece about a half inch wider than the base, plus the area for the “fence,” then cutting the plywood for a perfect “what you see is what you get” cut each time.
I’d make one for four foot cuts and one for eight foot cuts.
If I was doing a lot of precision cuts, I’d be looking down the track saw road. It’s a tool, so it’s an investment.