One thing an artist should consider is the longevity of their work. Some people don’t consider watercolor paintings “lasting” works of art when compared with oils on canvas. But there’s nothing I know to suggest that a properly framed and protected watercolor painting executed on quality paper with proper pigments shouldn’t last as long as any oil painting on canvas.
Using the highest quality paper is a given, as well as quality pigments. Also, when matting your painting, make certain your front mat and backer are archival. They should not necessarily be more expensive, particularly if you order and purchase them in quantities of dozen or more at a time.
All the items you use to frame and mat your painting should be archival… including the hinges used to secure your painting to its mat. Any kind of rigid backing can be used to enclose your painting in its frame as long as it is archival. It’s better if the rigid back fits tightly around the inside of the frame so as to keep out the dirt. I generally don’t paper-over backs of frames, since this hinders removal of the painting from the frame. If you do this, you end up dedicating the frame to the painting and therefore cannot recycle it.
Instead, I choose a tight-fitting rigid backing and bendable metal retainers that are secured to the inside perimeter of a wooden frame. For assembled metal frames, a different system of springs retains the matted painting and backer mat. The foam backer fits tight around the perimeter of the frame, thus protecting the painting from dirt. As long as your mats and paper are archival, and you don’t mishandle the assembly, your painting framed and matted this way should last indefinitely. Vertical IKEA frames are also very tight around the perimeter since they have added features on the backside to achieve this result. Finally, paintings should not be hung where direct sunlight can strike them. To avoid problems of this nature, you might consider selecting some sort of glazing which blocks out ultraviolet light.
When setting up an exhibit (or traveling about with framed and/or matted originals), I always bring along an extra sheet of acrylic glazing. If I don’t do this and the glazing gets broken or scratched, I’ll be compromised.
The way to minimize such compromises is to handle your paintings carefully. Protect them when you’re moving them about. Also store them with care in places where they are protected from the elements. When traveling with paintings in your car, place them face to face, cover them with clean blankets, and arrange them so as to minimize any potential damage.