Thanks for the pointers on the floor dampness testing - there's NO water vapor coming up at all - the french drain was strictly for surface water accumulation outside the foundation, we never did have an issue - and still don't - with the slab being wet in any way.

I did a bunch more research and this stuff:

http://www.rustoleum.com/Product.asp?frm_product_id=57&SBL=1

Seems to be just what I need.