I just did that on a sidewall for my 228D but did not make a vid. You can order the factory parts for probably $150 and another $250 or more to ship given the length is longer than mine. Forest River won't quote shipping.
remove anything on the inside of the sidewall. Curtains velcro'd at the top, screws holding the plastic strip with that secures the top of the tent to the sidewall. Mine had some above were the curtain attaches and under that part as well so had to get at them from the outside while lowered most of the way. Wiring for AC etc... Basically remove anything on the inside including the angled pieces on the corners that attach the inside corner to the inside of the front and rear panels.
Remove the thin strip that is on the top metal angle piece at the corner of the roof and sidewall. If you don't know what I mean its on the side of the metal angle piece and is black, press on the area you will see it moves. It seemed to shrink after I removed it so keep it stretched. Its just a trim cover for all the screws holding that corner piece on. Take those screws out. Using a plastic tool gently work your way down the underside of the trim piece between the roof and the trim. There is a dicor like sealant there to release. BEWARE!! The roof is VERY thin so go slow, and force nothing! Gently work your way from one end to the other. Do the same on the sides but they will release easier.
With that trim off you can get the corner caps off (buy new ones they are less than $5 each).
At this point you will have to support the roof so you can remove the sidewalls since they hold it up. I bought some 5 gallon pales with lids and placed them at the corners of the roof without the mattress as it will crush the heck out of it. Don't support it from the front/rear ends of the roof walls. There is nothing of substance under the rounded part of the roof so nothing to support it once the sidewall is off.
With the roof supported on the side you are removing lower the roof by about an inch. This will keep the side panel from pushing upwards when you fully release it. You can use a hammer and bang from the inside out of the sidewall to loosen the stapes that hold the side panel to the roof solid wood piece and sidewall ply. Once the staples were loose I used flat head screwdriver to pry it out enough to pull with vice grip (clamping) pliers.
Once the staples are all out you should be able to remove the 2 screws per lifter and then completely free the side panel. That is a 2 person job to be sure! If yours are as bad as mine was it turned in to a noodle so be careful with removal.
The gasket will slide out of the metal trim at the bottom of the sidewall, there is usually a screw on each end of the gasket right in to the sidepanel to keep it from sliding around so take those out before sliding it out.
Under that gasket are screws holding the metal trim on. Unscrew those and and work the trim piece off.
Clean up all the sealant from the trim to reinstall. I used this to seal the top/edge trim piece back on.
Apply one strip on the top and one strip on the edge and press the corners together.
I used stainless screws to reinstall the new side panel to the board behind it along the roof ledge and to the front/back plywood.
I was able to strip off the inside white plastic layer from the old sideboard to use as a template for holes etc... on the new one. You might be able to do that for shape too?
When putting the top corner piece back on once the new panel was installed I used a clamp to pull it down against the roof and press it in to the dicor to help seal it back up before installed a screw. A Long clamp with a block of wood under the bottom metal trim piece to make it square and easier for the clamp to grab.
I hope this helps.