I'd be careful about drilling holes into the wooden base to allow the Cellucaly something to bite into; if anything I think that this would only provide a more convenient and easy way for water and moisture to permeate the wood, which then willl give you warping. I'd advise against this.
I have only ever had one base pull away from the wood, and to be honest, I don't know what caused it. I have had wood bases warp on occasion, but that's usually always been the result of just not water-sealing them thoroughly. You're gonna get water-warpage on any wooden base if you don't seal it.
I add maybe a tablespoon or two dollops of white glue to a 3X4 plastic bowl of Celluclay that I'mmixing up, but more or less you gotta just make sure you don't saturate it with either glue, paint, or water. A little bit of experience and testing willgive you a good feel for it after a while; after that, it's pretty much gravy.
The comment about the "feel" of Cellucaly are correct; a nice, pasty feel is what you want--basically as little water as you can get away with, and you can always dip your fingers in water to smooth and shape it around, or just add a slight bit more to the top to make it a little smoother.