Using DAP Crack Shot and Dry Dex I applied a thin coat, sanded using a sandpaper sponge and then repeated. I kept repeating her advice that if you can feel the seam you will see it. Pay careful attention to any raw MDF edges. They also need a thin coat of mud. We did our best to design the trim placement so that there was as little as possible but was impossible to avoid everywhere. Raw MDF soaks up primer and leaves an ugly, bumpy finish so apply a thin coat and sand lightly to smooth.
This is what my office looks like. I have to put on my climbing shoes to get to my computer. I am so anxious to get my house put back together!