My exprince is to never use stainless together with Aluminium. The Al will just corrode and leave a pocket of white powder around any bolt treaded into the Al. If corrosive environment similar to wet winter roads with salt, I would say that you will fail with this material mix.
I can add to what is said previously that there is a material, suitable for high temp application. 153MA or 253 MA supplied by AVESTA. It may be considered as an overkill but does the job for many years, we uses the material at 800 to 900 C for more than 15 years in some applications.
You should check on MEGTEC.com web page they currently supply an RTO system to Australia with an embedded boiler in the RTO producing superheated steam.