Wet sanding primer is a no no in regular cases. I use to do body work on cars and we would never wet sand the primer, primer acts like a sponge and absorbs water thus trapping water next to the steel. HOWEVER in our application it's ok to wet sand primer as we have a layer of resin between the paper and the water. Still unless you are going to mold a part wet sanding primer is a waist of time, if you have it smooth just using regular sand paper the paint will come out just fine. Wet sanding is used after the layers of paint are applied to remove orange peel (orange peel is when you look at the part in the light and the surface will have tiny bumps like the peel of an orange), and make the surface mirror smooth. You then apply your layers of clear coat and buff that to a smooth mirror shin.
Great work as well.
Edit I also forgot to add you can NOT use that sander for wet sanding it will short out. Besides wet sanding should be done by hand as it is a delicate process, sand to much in one area and you'll remove the paint to the primer and have to start over. Also a Bondo tip: keep your layers thing and you won't have to do as much sanding, you can add more bondo as you go along. Makes for less wear and tear on the sander.