rust in fuel tank

[rpm197]

I have a 2002 7GCAA with less than 400 hrs. that I recently purchased. I have noticed small amounts of rust specs when sumping the right tank which clears up after several draws from the sump. Looking for the source I found rust around the inside of the filler neck and some on the cap itself. Has anyone had similar experience? Has anyone seen fuel tank corrosion or know what the tank is made of?

 

[jerrymjr]

Tank is all 3003 Aluminum.
The only steel is the filler neck. Likely the plating is not helping anymore. The fabric work would be the most annoying part, but swapping the part otherwise its just 10-12 screws and a gasket.