Jens
I've read about models using lithoplate in a number of English (U.K.) magazines - seems to be rather common. Some have been in 2 to 3 foot wingspan freeflight models. Seems to me that I heard that it does come in different thicknesses (different weights) so it could become heavy.
Flite-Metal looks like a very good and easier option, although I think lithoplate and contact cement will be much cheaper
Luck