What about placing the casing back-to-back? Might need a filler strip to make it wide enough.

Beth, yes! These are great, thanks so much.

It should match your other windows .

It should match your other windows. I like Beth's examples. Do it on all of the windows. It will look great.

Wider trim will require a new window sill so the whole trim assembly gets remade. Is this the only window that was installed? If the flat trim in between the windows is the major eyesore you could replace it with a beaded trim. This would have to be done with a router. Not usually an off the shelf piece of trim.

@PeterBRice, there is another window. Will post a shot when I get home. It seems to me that this double window needs more trim-they've got something for a single window. I agree we could ask for beaded trim but I think it doesn't solve the proportion problem. The casing is too skimpy. You're right, I'm into having to replace the window sill and everything.

All, I appreciate the feedback. You guys are so smart.