I gave up on priming with spray paint. Last year I went through so many cans of spray paint because they froze up while priming in 20 degree weather (this hobby/obsession doesn't pause for cold weather). On top of that, I never did like priming with spray paint because I either missed spots or put it on too thick trying to get every nook.
Spraying while the parts were on the sprue helped a lot. But I still had to redo it after putting the model together to cover the sanding and cut marks. Then, I special ordered some missile launcher IG from the War Store, which didn't come on a sprue but instead a little bag of parts. How the heck was I suppose to prime them?
So now I prime with a brush. I don't know if there are special primer paints out there and if there were I would probably be too cheap to buy them. With that said, in order for the brush-priming method to work correctly, you will need to put out some money on a good brush and Citadel foundation paint.
After cleaning the chunks off the model, sanding down the mold lines, putting it together, then denting/scratching/weathering/wearing down the armor of your model, put a layer of foundation paint on with a tank brush. It doesn't work to well with any other type of brush - you will just leave marks and lines. Work the paint into every hole, crevice, and armpit with the tank brush ensuring that you are not leaving any paint standing. The paint should be put on thin. Really work the paint into the model. This isn't detail work you're doing. Move the brush in circles and press it into the recessed areas. It will be tough on the brush, but it's worth it.
Remember to use a lighter color foundation (such as Dheneb Stone) for white or light colored models. Depending on the color foundation you use, you will may still be able to see the gray plastic or metal. Wait until the first coat is completely dry before applying a second coat. This is where batch painting helps as you should wait about five minutes before applying the second coat. In many cases a second coat isn't required unless you put the foundation paint on too thin.
When the primer is dry, then apply the main color of your model. Use the majority color of your model for this layer and cover the whole model. This is part of the primer layer, so ensure you cover every area. If your majority color is watered down like it is suppose to be, then this will take at least three coats. Again, use the tank brush and put on thin layers.
When you are done, you will have a completely primed model that will also have you foundation color. If your majority color is darker than the lightest color (such as skin), then you will want to use a light color foundation paint on those areas prior to the actual color layers (just like you would using the "spray" priming method).
The advantage, of course, if that the production of your army doesn't slow down during the winter months.