I built a partial grille block from a rubbermaid office trashcan and zip-tied it to the grille for my Jeep MJ, pictured. Since the 2.5s run hot I did not wish to block it entirely for year-round daily driver use.
Also shown a homebuilt lower air dam which was made from an 80s S-10 air dam riveted to the factory one; it is reinforced behind with angle iron mounted to the sway bar mounts. The dam does not quite go down as far as I would like as the lower control arms are still visible... but both the dam and grille blocks have held up since 2014 with no issues. I have since gorilla-taped the gaps above and below the bumper, which has also held up despite it being tape.