Have you ever had that impossible to reach crack where you just can't get your caulking gun in?
Try taping one of those oversized ice drink straws of some small diamater tubing onto the end of your caulking gun. Make sure you have it well attached, you don't want it squirting off and making a mess.
Use a caulking that is easy to gun, like a silicone or acrylic latex so there will be less resistance as you force it through the straw.