A good question, I always paint them apart. Paint the inside semi-gloss to look like unpolished lacquer, mask the inside up and then paint the outside. This way you can sit the panels on a bench. I use 3 qt cans to hold them up off of the surface. (One can at one end, two at the other, like a triangle) It take more time but less chance of having them fall. Also a trick to take out the centre rod that's hollow. Put a drill bit inside of the tube leave it sticking out about 1/2" then clamp on to it with a electric drill and turn it out. Learn't that one from a Model A guy about 40 years ago. JP