If the wood is the most common type - CCA pressure treated - the issue is the moisture content of the wood. Not only does wet wood make for a weak bondline, it is also very dynamic and will move and twist as it dries. The copper component is not the issue.
Given that its a trailer and will not be submerged for long periods I would advise against using the treated lumber use untreated lumber, encapsulate the parts with a couple coats of epoxy and bond the beds to the wood with G/flex 655. Everything should get painted as the last step for longevity.
I think what I'll be doing is epoxying in a pad, say 1 foot x 1 foot, that will match the cradle, and then use the treated 2 x 10's to mount the pads to the trailer, so the 2x10's will run the length of the trailer, and the cradles will rest on them. So I'm not going to epoxy the 2 x10 stringers; I'm sure for the number of times they'll be submerged, or even wet, won't affect much at all. I'll continue to monitor of the cradles are getting warped at all every so often by lifting the boat and looking for fit, but again, it's not that heavy a boat. Thanks for the input... I figured if you cover wood with epoxy, the moisture content just stays the same, kind of like suspended animation.