We also have a 2108DS and I added piano hinges to the seat covers. I did not do it the way I saw it on the forum with the hinge screwed to the back wall. Here is was I did: removed seat cushion, raised plywood seat to rest against the seat back cushion, I took a measurement with the seat sitting up, 4-1/2. I took the plywood to my shop and cut a 4-1/2 strip off the rear of both seats. Next I purchased 1x 2 pine, a much better grade then Winnebago used. Measured, cut and pocket hole drilled the new supports, installed the supports. I applied 3 coats of high-gloss paint to all sides of the seat cover. Next I clamped the 4-1/2 strip to the back of the seat frame, make sure you have clearance on both sides and the front is flush with the new support. Use a flex bit or extra long bit to drill the rear holes so you dont scuff the wood panel or wall, remove strip and counter sink seat top. I used #8 1-1/4 exterior deck screws. Install 4-1/2 strip and screw it down. Also notch the front of the seat lid so it will clear the window cord post. Next take the seat and set in place as if raised and mark the location of the factory framing on the bottom of the seat, make sure you are lined up with the rear strip and the seat clears the wall and the rounded side. Now the hinge, I used a 1-1/2 x 42 stainless steel hinge from
www.boatoutfitters.com you can order any size from them. The holes on the hinge are 2 on center, so just lay it out to clear the factory framing. Next I clamped the 1 x 2 support and hinge to the rear of the seat making sure I had clearance from the factory framing, I placed a cardboard shim between hinge and the seat and support for clearance, fold the hinge down on the shim and clamp hinge on the the seat. I drilled all my hinge holes with a Vix self centering drill bit, install #8 screws. Take the seat out to the camper and line it up with the 4-1/2 strip, raise and lower to make sure everything clears. I put shims on the front and sides before drilling the rear hinge holes with the Vix drill bit, Install screws remove cardboard shim and now it time to do the other seat. Ive attached a few pics. Hope this helps Ron