I finally got tired of looking at the 30+ years of bandaids sitting on top of my belly band and decided to do what the factory should have done in the first place; eliminate it.
Here's a step by step:
Tools- 4.5" angle grinder
palm sander
drill
pliers
respirator
ear and eye protection
chisel
widget
Suplies- Bondo Glass (short strand)
Bondo Ultimate body filler
Bondo spreaders
80 grit flap disc for grinder
80 grit sanding pads for palm sander
nitrile gloves
rags
stir sticks
paint roller trays
ultra smooth high density foam rollers and frame
denatured alcohol
enamel reducer
grey lacquer primer
paint-Omni AE acrylic enamel, Isuzu Parthenon Ivory #91110
First step- Remove old belly band. Mine mostly just pulled off but, you may need to drill out some of the rivets.
Pretty ugly under there. If you think your's doesn't look like this, I got a river in Egypt I'd like to show ya.

The next step is the most pain staking of the whole project; removing the 30+ years of silicone, caulk, silicone, caulk, ect. I used a chisel, a widget, and elbow grease. I didn't worry too much about residue because I knew the most of the surface was was going to be ground/sanded away.
All but one of the metal plates were totally rusted. This corrosion had reeked all kinds of havoc with the glass that was surrounding them, leaving big bulges and irregularities all over; I highlighted them with a red marker.
Next I went to town with the angle grinder/80 grit flap disc. My goal was to create a "below grade" trench throughout the center +/- 2" of the belly band area, and expose as many of the rotten metal plates as possible, being careful not to disturb the inner layer of glass holding the camper together. This was DIRTY, nasty work. Respirator, gloves, headphones were a must, a full tyveck suit would have been a good idea.
Yank out as many exposed plates as possible with pliers.
Now I cleaned all exposed areas with denatured alcohol, and filled the main seam and all big holes with Bondo Glass. This stuff kicks fast so I was was only able to mix/apply about a golf ball sized glob at a time. By the time I made it around the camper, the starting point was ready for sanding. 80 grit on the palm sander was perfect.
Next I cleaned with DA again, filled all remaining low spots with Bondo body filler, sanded, filled, sanded, until flush and fair. This took me about 4 coats, each easier than the one before it.
Now I cleaned the area yet again and prepped for
painting with blue masking tape.
Into the
paint booth! (It started raining) Rolled on the primer.
Lightly sanded the primer, cleaned with a damp rag, then rolled on the first coat of
paint. I rolled on two coats and was unhappy with some bubbling I was having so I let it dry overnight,
light sand to remove the offending bubbles, thinned the paint just a touch with enamel reducer, and rolled on a final coat. Perfect!
I think it turned out pretty damn good. I'd had no prior autobody/fiberglass repair experience. It took me 3 days but could easily be done in a weekend with this as a guide.
Don't be afraid!
Scott