I have just started bringing my watercolors on trips. I have a bin of brushes, palettes and paints which I can easily stow and a small portfolio for sketchbooks and paper which slides into a closet.
Watercolor is extremely portable. You can throw a small palette, a watercolor sketchbook, pens, a few brushes and a bottle of water in a pack and off you go, ready to stop and sketch/paint anywhere. A cell phone can make great photo references. I have been looking at some easel set ups from Sun Eden for plein air, but so far a camp chair and my lap work well for field work. In the trailer, I can set up at the dinette with photo references and work to my heart's content. My long term goal is to document our trips in watercolor sketches. It's still a goal in progress. Sketching on site is really fun. People may stop by out of curiosity, but that is part of the fun. I do stay off to the side so as not to block a path.
Cathy Johnson's blog and website has many tips for sketching and painting in nature. Cathy Johnson--Art, Life, and other Oddities
All the best,