Yours is way nicer than what I make, I take a piece of plywood, OSB and 6 chunks of 2x4, 2 are 16" or so and 4 are 6" or so.
p
p
p
p
p
p
p
p
p
p
P
SSSPSSS
LLLLLLLLLLLLLLLLL
P = plywood
S = 5" 2x4
L = 16" 2x4
Basically the two shorter pieces are screwed to the longer board so that they wedge the plywood so that it stands up but it is easy to pull out an lay flat for storage. combine that with a foldeing shooting bench and a range is anywhere you have space.