I found the full wall panel inside of the bay window a bit overwhelming. It's lovely but I never felt it matched the rooms I was making. So I trimmed that away (along with a bit of excessive exterior panel leaving a simple window frame that allows my wall paper choice to show. This required making a new window base with a custom wall cut-out.
No expansion packs are required for these bay windows.
Bay Windows for Decorators (hacked
Why "for decorators"?
To place an object on Maxis' bay window you must actually put the object on the INSIDE window tile. The window then shifts the object over so it appears to be on the shelf but the Sim still knows it is inside. The "for decorators" version places objects OUTSIDE so be careful what you place there or you'll have Sims reaching through the window graphics. The reward for this minor inconvenience is the ability to place furnishings along the interior wall right below the window.
Object Makers' Note: As bases these objects are particularly suited for privacy fences and tall walls simply because they drop with walls. There is nothing about them that requires they remain a fence. Remember to re- categorize them if you change them to something else.