I am not about to say anything is impossible in the digital world, however, for an easier watercolor effect, I would turn to Artrage or to Rebelle - not sure if I'm spelling the later correctly, but there the paint runs like watercolor. In art rage I use the watercolor brush and then use a few different blenders using the wet palette knife tool, that give a slight frosted texture. The watercolor is definitely wet and will blend unlike Photoshop or Illustrator. Both Artrage and Rebelle have a free trial and are quite affordable. Corel Painter is another good program for watercolor. However, it is a lot more expensive, and more involved than using Artrage or Rebelle. I find painter overwhelming - too many controls.
Take a look in the Digital Showcase for painting effects that you are trying to achieve, and feel free to ask the poster what programs they are using. People here are friendly and willing to give advice.
I'm just finishing up a watercolor of an old rusting car. I'm not sure I'm finished yet, but I'll attach it, just to give you an idea what art rage can do.
Welcome, and I hope you will tell us about some of your adventures in Illustrating.