Did a painting for my husband’s custom bass a while ago. He made the bass from parts, and I painted the painting on heavy watercolor paper and mounted it to the bass.
The painting is gouache paint sprayed with quite a few coats of Krylon Crystal Clear Acrylic coating, and then waxed with Dorland’s Wax Medium (to reduce sheen and prevent acrylic tackiness problems). Mounted the paper to the bass with Golden Acrylic Soft Gel.
Painted it probably a year ago or so and the finish has held up well to regular usage.