Coat your dividers in as many layers of this as you can get out of the tin.
Automotive filler primer is the best thing in my opinion for getting a good finish on decorative things like this when using MDF.Sand it down when dry and do it again, the more time invested on this early stage the better the final finish will be. Seal your mdf with a mixture of PVA and water to minimize the amount of primer you'll need, MDF is like a sponge on the cut edges.
