I'll be watching with interest your repairs because I have an Argosy 28 that needs the front floor section under the gaucho/fresh water tank replaced, too. This started from a crack in the fresh water fill. If you want to see a gory photo of the damage, look in my gallery toward the end of the pictures.
Hopefully somebody who has done this will chime in here, but I've read about it being done both from the top alone and with top and bottom access. Since I have a wide, curved section to replace, I'll be going in from both the top and bottom. This will require removing inside skin segments (which I've already done and which is NOT difficult) to access the C-channel that the floor is mounted in and bolted to.
I also have a bad spot right in front of the door where the door seal leaked. Since I need to have some welding down on the step, this will also be a job done from both sides, although it probably could be patched from just the top.
1975 Argosy 28 "Argosy"
1979 Excella 500 31 "Betsy"
1992 Lincoln Mk 7 LSC
2003 Dodge 2500 Cummins "TowHog"
"Lucy Loosehair" the cat - Airstream mascot
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