What mufflers should I get?

[Silvapain]

Stainless steel doesn't rust.

Actually, it does "rust".

"Rust" is better termed oxidation, or the bonding of the base metal with oxygen. Iron often oxidates to Fe2 O3 - Iron Oxide, or "rust".

Stainless steel is defined by having a minimum of 10% by mass Chromium. The Chromium forms what is known as a "Passivation Layer" of Chromium Oxide (Cr2 O3) that is so thin that it is invisible to the ***** eye. This Oxidized layer prevents the rest of the base metal from oxidizing.

Aluminum also passivates like stainless steel.

Paul, 403 is a type of stainless steel. It has a relatively low Chromuim content and a high carbon content; making it very strong, but not very corrosion resistant.
http://www.efunda.com/Materials/alloys/stainless_steels/show_stainless.cfm?ID=AISI_Type_403&prop=all&Page_Title=AISI%20Type%20403