My first - and I guarantee last - experiment with copper electroplating. Ruined a couple already-etched enclosures, my favorite pants and spent 8-10 hours swirling it in the copper bath and polishing it back.
Aluminium is well known for not being nice to plate on to, for the same reason you can't solder on to it. It forms a highly unreactive, insoluble oxidised layer really quickly, so copper and/or solder won't stick. It does mean that aluminium is very durable in terms of corrosion though.
I think the best way to plate copper (or other metals) on to aluminium would be to put it in your bath of copper solution and connect the power up with the enclosure connected to the + end of your supply, etch away the surface of the metal, then switch the power leads around without removing the aluminium from the solution. Normal surface preparation (lots of sanding and a clean with acetone or something before the etch/plate, etc) would need to be done to a very high standard.