no, seriously!
You have one arc that could be done with stacked MDF, and the other surfaces are flat. Only real tricky part is the slanted side with the stairstep at the bottom. But if you're good with your tablesaw and angle measure-er, should be GTG.
I'd use 1/2" MDF and/or 1/2" baltic birch. Prolly baltic birch cause it's so small.
Tho your job would be monumentally easier if you found a way to magically move that amp.....
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BTW, is the car 100% done minus the subwoofer? Maybe subwoofer and wiring cleanup?