I have chosen an astragal as the base molding. I am using a Sargent 1080 with a wide beading iron to make a bead a little in from the edge. This helps to guide the cut straight. As with any plane of this type (plow, dado, bead), it helps to start the cut at the end of the board and make the first few passes gradually longer until you are planing the full length of the board.
Here's what the board looks like when the bead has been finished. Make enough to get all your pieces from one length if you can. Also, make sure you have enough to discard about 6-8" from each end as the ends usually have some dings from starting and stopping the planing stroke. Now I need to separate the bead from the rest of the board. I could rip it off with a saw but......
Using the smallest plow iron you have actually works much better than sawing. Simply plow a groove from both side that meets in the middle. Once the molding is separated from the main board, you can clean up the plowed edge with a few simple swipes of a plane.
Then use a chisel to pare the extra wood off the fillets of the astragal leaving only the bead standing proud. It will surprise you haw smooth a surface you can get just using the chisel. There will be some small facets left when you are done but I like this look. You don't really see it until you look real close or feel the molding, but it gives a nice hand made touch that doesn't look or feel like it came out of a machine.
Once you have the long length of molding done, miter one end of the front piece and gauge it's final length off the front of the case.
Then fit the side moldings the same way. They are trimmed to length at the back after the miter fits well.
Finally, attach the moldings with nails. Add some glue at the miters to keep them from separating.