I have been studying the outline planning application for the old Vauxhall site at
http://www2.luton.gov.uk/kimptonroad/. The proposal includes a 24m high mega multi story car park for the airport, which will contain 5000 spaces. The location for this is at the back end of the development in the northeastern corner. Location maps can be found in the development framework plan. Also worth looking at the Development concept aerial prospective link in the mauve section