Hello Joe1261 -- There are almost as many methods to repair as there are members. You seem to suggest the area is in the front only. First job is to address the source of water that caused the rot. A couple of floor repairs I have done are covered here
. Argosy & Airstream were built just about alike. You will need to remove the perimeter trim (rubrail), banana wrap near your repair and drop some of the belly wrap. Re-use the curved corner banana wrap!
B.A.L. stabilizer fastener bolts and elevator bolts holding the floor will be corroded into the frame and frozen -- grind flush and drill new holes alongside if necessary. Some of the belly wrap you loosen can be reused but it was thin .025" to begin with and will no doubt have areas damaged by corrosion. Belly wrap was originally one piece -- you'll do yourself a favor if you don't involve that at mid trailer where the gas line feeds go up. You will be drilling out and replacing a lot of aluminum-core pop rivets (Olympics are only necessary to repair the bucked rivets seen on the body above the rubrail). You'll want to Por-15 the A-frame when you have the front opened up.
Can you work on your Sovereign
at home? Lucky... Keep asking questions! I know there will be a lot of them.