In order to groove the bottom rail, I set my double marking gauge to the width of the plow plane blade.
Then scored the edges of the groove to prevent tear out.
Using the plow to make the groove.
I used a Paul Seller’s work holding method and a Rockler clamp to hold the board while I plowed the groove. I was pretty happy with how well it worked. I clamped the edges of the piece in the clamp and then clamped the clamp in my vise.