Here are two more idiom drawing/paintings from last week:
I mounted them on panels that I'd coated with a deep, dark blue acrylic mix. Then I glued the paintings onto the panels with matte medium. Once the matte medium had dried a little, I coated the painting with two coats of a thin, watered-down layer of matte medium. The matte medium securely fixes the watercolor and gouache, and should give the piece some UV protection as well. You just have to be very careful to spray fix the painting before you apply that top coat, and then be very, very careful and gentle as you brush the gel on top. Otherwise the gouache will smear like crazy. When that happens I just touch up the painting with some acrylic.