We use 24” x 16” pieces of Luan plywood for target backdrops. We get 12 pieces from a 4x8 sheet. We slide then down between angle irons, set into the ground 16” apart, on the berm above the railroad ties.
I would investigate using the ‘U’ channel that holds unfinished mirrors, top & bottom, to doors. If they’re screwed on the top and bottom of the target frame, one can just slide a piece Luan plywood, or corrugated cardboard or plastic, or something, in from the side.
"Sometimes I pretend to be normal, but it's boring and I go back to being me."
"You might as well be yourself, people won’t like you anyway."
"Tres verbo dictom"