I make my door inserts as two pieces.

One piece is the "show panel", usually 3/4" thick, it's the door that you actually see. The assembled stiles, rails, raised panels, etc. All painted or stained up purdy.

The second set of pieces I make combine the .10" spacer and the .25" panel in one. I usually rip roughly 2" to 3" wide strips of 3/4" poplar on my table saw. I'll rip a 3/4" thick poplar board to say about 3" wide. I then reset the fence to just a tad under 3/8", flip the board up on edge, and run it through so I now have ~3/8" shy thick by 3" wide strips of poplar.

Now I rest the fence to 1/4" from the blade and raise the blade to about 5/16" high. I then run the strips through. This will waste away something like a rabbet, roughly .10" by 5/16".

This poplar strip now serves as both my .10" shim and my .25" thick backer panel. I attach them to the back of my door panel, around the perimeter of the panel.

Hope it makes sense.

Mongo

Yes, that makes a lot of sense! I see how I could do that, or a modification of it (I'm actually makig my "show panels" out of six different pieces) for my project.

Thanks!