I've laid up fiberglass compound corners inside hemispherical steel barbecue lids found at metal recycling centers.
I've also run schedule-40 PVC pipe through the table saw to create molds for the corner radii.
Thermo-formed ABS plastic fish ponds have some fabulous compound forms of which the inside surfaces could serve as molds.
Tractor Supply also carries cattle troughs which are thermo-formed ABS which possess both compound corners and edge radii.
And children's poly tubular playground slides have compound curves almost as large as what Airstream and Argossy trailers use.
Flea Markets,yard sales,junk dealers,Habitat for Humanity Resale stores can all be sources for what would otherwise be extremely expensive 3D forms.
