Not sure what the thickness of 12 gauge aluminum is, google tells me its ~.080" which is really thin to be exposed to the stresses it'll see bolted to a vehicle, and not the easiest to to weld, constant dynamic beating by the road is going to fatigue those welds in no time if its .080". FYI Typically aluminum sheets are purchased in decimal thickness. I would assume the main plate of the diffuser is at least .100" maybe .125" for extra strength. This calculator is a good recourse for sheet weights.
https://www.onlinemetals.com/en/weight-calculator
Dastrup you going to vacuum your oil out for oil changes or drop the diffuser?
Sometimes I wish I was still at my old job, but only when it comes to making **** like this, could have made it out of our scrap material.
32" x 48" x .125" sheet in this example (18lb), with .125" thick fins total weight is 25# inner fins looks thinner in Dastrups pics, but whatever.
.100" AL for all components, 20# total.
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