Enlisting the help of Brother Dazco of "Jambo" fame we started with the o/s lower panel and thought it a good idea to show some photos before , during , and after replacement.
1st photo shows the o/s of Snowie..lots of rust around the lower vent, and an odd looking extra vent has been previously added for some reason. I tried to rotate photo on photobucket without success

Inside view showing lots of rust and filler. fortunately the floor is in good condition:

Outside view with vent removed and what we found behind the extra "vent"

Yes this really is filler used to bung the rust hole up below the vent:

Will add a few more pics as the job gets underway.
Paul