A welded Al ladder chassis would be fine. Box section for rigidity/strength, TIG welded and anodised. Cost of materials and anodising would be up t not hugely so.
The chassis would need suitable beefing up at key points..front cross brace attachment, engine mount, gearbox mount, rear axle mount etc.
Structural grade Al alloys are fine....planes are made that way!
As for an Aero style tub....repair extremely diffucult unless it were designed in sections that could be separated and a new one attached. Definitely not a job for the amareur, even most repair shops.
Modern paint systems are hugely improved over the old cellulose type from years ago, and electrophoretic dipping processes help enormously.
The biggest problems with older cars were down to poor design issues resulting in crevices to concentrate wet areas and mud pockets..remember front wing corrosion round headlights? Poor drainage of cavities...sills,doors etc.
I remember them coming into the coachbuilders my dad worked at and him showing me the rust hotspots on cars.
Dinitrol is good stuff. I particularly like the way it retains plasticity and doesn't chip.
