I have several questions. First, are the nails galvanized or stainless steel? If they are galvanized, I would prime them first with Ospho before caulking and then prime with a regular primer. Ospho is a green liquid that will turn rust black and prevent bleed through on your paint. Galvanized nails rust fairly quickly and this will head off a problem in a year or so down the road. You can also use Hammerite Rust Cap Primer for the nails. (Many painters tell me that QTips work great for applying Ospho). If they are stainless, I would caulk first and then prime the surface. This will prevent any flashing effect from the Ospho on the finish coat. I would actually prefer to use a spackling compound that will stay somewhat flexible, but you can use caulk also. Is the siding a hardi-panel or hardi-plank? I have not seen any real wood siding pre-primed in my market. If it is hardi-plank, I would prime the siding with a good latex 100% acrylic primer. You could use 123 by Zinsser, Suprime by Pratt and Lambert, or FreshStart by Ben Moore and then topcoat with your choice of paint. Every paint company will manufacture a 100% acrylic primer to use with their topcoat. The primer used on siding as well as steel doors is to protect the product in shipment. It is still intended to be primed before painting. I would highly recommend that your primer be manufactured by the same company as the paint for warranty reasons. Make sure you use a really high quality caulk. I have found that Big Stretch Caulk by Sashco is the easiest to work with of all the caulks on the market. It is paintable. It is a little expensive, but is very flexible and smooths out great. Consider having your primer tinted 1/4 to 1/2 formula of your topcoat color. It makes the paint cover better. The primer will still be a little light to the finish coat so you can see any areas you have missed when applying your topcoat. I do recommend two coats of finish paint.

I have to admit that it is kind of a pain compared to other materials. The biggest problem is that you need to wait a week to paint it. It is nice that you can paint it or not and it is supposed to be more durable than silicone or latex. I don't see the chasm. The English definitions of caulk and sealant are very similar. What is the difference in your mind?

I'm a contractor in ny who just installed white painted cabinets for a client.. counter top installer just finished installing... the following day along the entire perimeter of cabinets are now a bright neon yellow color??? trying to find why?? obviously there is some sort of chemical reaction between the silicone and the paint. does anyone have any information on this issue please. I can be reached at 631-433-1614 thank you in advance for. Ed

@Sombreuil - understood. Mostly, observed when 2 trim pieces came together at a corner & the prior caulk or paint in that corner had opened up. My only real concern, is that this is a yearly thing since I had thought these new space-age caulk supposedly hold up longer than 1 year. And the last time we did this type of caulking was last spring. So maybe as @rwiegand says, i should wait till it's driest to have the largest gap to fill due to shrinkage vs. when it's humid and things expand & leaves the cracks smaller.