Instead of aluminum foil consider using kitchen cling wrap. But lots of people seem to get by with more conventional mold release compounds like wax followed by PVA.
If you want a step by step by step by step (ad infinitum) primer on making composite motorcycle bodywork take a look at
SV Carbon Tank project for Zoran - BARF - Bay Area Riders Forum
Very detailed discussion, lots of photos, well worth reading/bookmarking.
cheers,
Michael