Here's a couple of pics from one of my hand built cars where aluminum was riveted and bonded to chassis tubes.
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View attachment 134960
The aluminum used was 3003 alloy and .050 in thickness. For the engine compartment panels, I used anodized aluminum which I'd recommend for panels that are highly visible because it won't oxidize and is easy to keep looking nice with a spritz of detailing fluid. I happened to find a sheet of clear anodized aluminum at the metal supplier that they sold me for plain sheet cost. I'm guessing I got lucky and you'd likely need to special order the anodized sheet and it will come at a premium cost. Even so, probably worth it for some portion of the project if looks are a priority.
Since building that car, I have more experience with other aluminum alloys. I'd recommend using 5052 alloy for this type application. 5052 is marine grade aluminum so more corrosion resistant. It's not as easy to form or metal shape as 3003 but most chassis panels are flat or have straight folds in them. 5052 is also just a bit less expensive than 3003. For general fill panels I'd recommend .040 or .050 thickness. If you want more torsional rigidity, then .063 or even .090, it just weighs a little bit more.