Sealing mixed mediums: sand, fabric, paint, on wood
In a nutshell, I've got 3 planter box for mini gardens that I want to finish so they will last a few years. They are made of treated wood, 1 1/2" thick. They have holes for water to drain, and will house succulent type plants that need very little water and soil that does not have much moisture in it, so will not be soggy but may be rained on occasionally, if very windy.
#1: Acrylic decoration painted on raw wood.
#2: Need suggestion for substance to cause sand to stick to outside of box.
#3: Need suggestion for substance to cause squares of fabric to stick to outside of box, to look like a quilt.
The concept I want to exploit is like when you go to a restaurant and the table has pictures or whatever objects decorating it, encased in - plastic?
I would like to seal/waterproof all 3 boxes after above-described decorations are complete. Polyurethane? Can I use multiple coats to make it feel smooth?
I'm completely stuck, have not done much with wood before.
Thanks for reading and any advice/opinions/suggestions!