no problems....I did mine with .5 mm aluminium sheets. Pretty cheap. made a huge difference on the low end (which sucked after I installed an Apexi Pwer Intake).
Use a cardboard to first do a template, trace it onto a alu sheet and cut with a pair of garden shears. For inner lining I used some industrial rubbet sheets, maybe not necessary. mail me and I can send you my DIY document (too huge to attach over here)
Mines a 200SX S13 CA18DET.