When I say make panels, I don't build them any more. I enjoy making them, but find it takes me way too long to build them proper. It is just easier for me to hire someone who knows what they are doing make quality cradled panels for me. I have them custom made for me from someone in the East Bay. He does great work and I get nice quality cradled panels. All I do is prime the surface.
I use gesso as my ground. I lay down about four or five layers of gesso sanding between coats to build a nice base. Then using a squeegee I work over the surface until I get a nice smooth surface. This a long process but after it is done I pleased with the results and am ready to paint.