Yep, lot's of good advice and I will throw more into the pot.
Firstly, if you use rivets, Monel is the material of choice. It is high strength, low corrosion
with both SST and Alloy. IF you use a blind rivet, then ensure you have a SST shaft thingy. That is so the head
remaining in the Rivet won't rust. IF you use an open Rivet, that shaft thingy will most likely be nickel plated. So you need to punch the head back out when it breaks off.
SST Rivets are the next choice, but can corrode in the alloy, if Salt water
can get to them. Stay away from Alloy rivets, the just aren't strong enough if in a high load situation. You could use them in a load load.
Threading should only be used when the load is not in a direct pull. Side pull or low loading is OK. Same with screws. In high load and direct pull situations, you always need a nut and washer on the back. A good size rivet will outperform a thread or screw.
The next thing is the fixing and insulation
of the Fitting. Place a thick smear of an adhesive sealant
, such as Seka Flex or similar product onto it. This will ensure a good bond other than just the Rivets, and also isolation from the two metals and water
can't get between the surfaces. Then when it is all fixed in place, wipe the thing down with a thinners or some solvant to wipe away excess sealant
to make it all look tidy.
When drilling, cutting or tapping Alloy, use WD40 as a cutting fluid. It doesn't require much, but it does require it often.