Go to your local skateboard shop and ask for a sheet of "grip tape". one sheet is about 12x36 and it's like thick sandpaper, but the adhesive used for skateboards is super sticky and water proof.
There are gun companies that have taken this idea and marketed it. Like Trugrip and Pachmayr, they make similar products at 10 times the cost of skateboard grip tape.
Guy-Harold Smith II