Stainless is better as it is much more resistant to corrosion and oxidation. Also, it is not good to use different metals together. Corrosion can be caused simply by dissimilar metals. Here is a list of metals that can cause corrosion to each other. http://www.galvanizeit.org/showContent,173,215.cfm I am not saying it wont or cant work, just that it could have undesirable effects. If i am correct, the copper will corrode while the SS will not. Also, since copper is very soft, the use of NaOH or KOH may destroy the copper. Of course, the only way to know for sure is to try.
2006 Ram, 5.9 cummins HO. 4 cell design, 1.5 LPM@30amp, 24.3 MPG