The thing that does worry me about the copper is the fact that it can oxidize if not protected properly. This distribution block/rail will be in the engine compartment, copper does offer the best conductivity but in this case would it be better to use aluminum or stainless steel.
As mentioned above, I think the only place that would be a concern is in the actual connection point. Which after connected, the area would be air and water tight not allowing any chance of oxidation in that critical area.
All other exposed part would only oxidize to a certain degree and then would be protected by the actually oxidation layer (this is why copper water pipes don't corrode into nothing over time and why copper is used in the exterior hull paint to protect ships).
If an area that has oxidized need to be used later on, then just fine sand it clean.
ALTHOUGH!, this only applies to water and humidity protection. Battery acid or any other chemical in the area might be a different story.