I do what Bill does, and have become a big fan of the stuff. In fact, I don't think I'll ever cover open bays with just silkspan again. I use light silkspan over laminating film, and don't believe there is any significant weight penalty. The minor additional weight of the SLC is likely offset by not needing as much dope to fill the silkspan, and there is a huge increase in resistance to the sort of stupid irritating little punctures that I seem to specialise in.
I've also just painted the film after wiping it over with acetone, with good results, although I agree with Bill that ultimately you mightn't get as good a paint job.