Using stainless steel screws on aluminum. While you might see some corrosion in the form of rust on the stainless steel screws and rust stains on the surface of the aluminum frame this is not caused by dissimilar metal issues. As was just stated by another forum member those two metals can be used together.
What actually is happening is many of the less expensive stainless steel screws purchased in bulk that are used by some of the RV manufacturing companies is of a pretty inferior quality of stainless steel that is prone to rust versus a high quality stainless steel screw. All stainless steel screws are not made of equal quality material.
When moisture gets trapped under the screw heads or is trapped in situations such as screws being under a vinyl screw cover trim strip then those screws begin to rust. When a Stainless screw is driven into wood the water on the wood can wick under the screw head travel down along the threads and then cause rust on the shank of the screw and weaken it. I have seen this situation on my Sunrader as well as on my Trails West Campster
. It is a good idea to put some marine bedding compound onto those treads and just under the head of the screw to keep the moisture under control. This will help a lot to reduce corrosion on those lower quality stainless screws. How would I know how good a quality of stainless is used in a screw I buy in a bin at the hardware store? I don't know and I can't find out other than if I see them rusting up fairly soon.
But I can purchase a known to be better quality screw from a local screw supply company and will of course pay the premium price for them but I have to purchase them in bags of 100 and I don't have anywhere near 100 stainless screws of the same length on my Campster
. So I will just get them from the hardware store and keep an eye on them and use bedding compound on them which also helps keep the stainless from bonding into the aluminum over the years.