built-in entertainment centers, window in the slideout, power tongue jacks, storage drawer under the frame, Maxx-Air fan covers, PopupGizmos, Reflectix in windows, Oxygenic shower head, splash guards in shower pan, 12v outlets, just to name a few.
most can be found on RV.net's Hybrid forum, since it's the most active hybrid forum.
My mods, Maxx-Air II, hand rail , door cross bar, Popup Gizmos solar covers, shower head (not the Oxygenic yet), and a Tornado Tank Rinser. I plan on installing a Fan Mate and a screen grille on the door.