Measure the windows in the camper shell. Purchase roller blinds that are wider than the window.
Unroll the binds completely and lay on a flat work surface. Pop one of the end caps off the blinds with a screwdriver. Set the cap to the side.
Mark the new width of the blind. Do this at both the top and bottom of the blind, as well as several points in between. Use the yardstick and pencil to make a line connecting all the marks.
Cut along the line with a utility knife, using the yardstick as a guide. Remove the excess blind material. Use the hacksaw to cut the barrel the blind attaches to.
Replace the end cap that you removed earlier. Roll up the shade for installation in the windows of the camper shell.