hmm... i would think sheetmetal would be easier, from the flex and little random abuse that offroading does, a sheetmetal one would be perfect, i saw it on powerblock, i think on muscle car? i would think just get a sheet that is the same length and height as ur radiator(minus the sides) and then add on about 2" (or how ever thick the fan is) to the top/bottom and sides, then on the corners,cut a 2" slice spliting the corners evenly in half (45*) then bend them at 90* so it looks like a big baking pan.and it should be 2" away from ur radiator and fit the size of ur radiator, o ya, then cut the circle(s) for ur fans. ill draw a picture if im a little confusing.