I'm at this stage as well.
Has anyone had trouble with MDF warping when they apply primer? I've heard this can happen and wanted to avoid it.
I read somewhere that you can make a mixture of yellow glue and water (1-to-3 ration) and apply it first to the MDF. Then let it dry, sand, and apply the primer. Of course, if nobody's had this problem (MDF absorbing primer and warping), I'd like to avoid the extra step.
Any thoughts?