Shrinkrap, hot dry and clay soil doesn’t sound good for any tuber! Large pots should work fine, and I’m guessing 5+ gallon pots will be needed. Dahlias like very good drainage, so a good dose of perlite in the soil should help. Also, no saucers under the pots; that could start rot.
You might need to give them a little shade, since CA sun is very hot. They didn’t flinch with days here in the 90s. The cooler you can keep the root zone, the better. Maybe plant a decorative ground cover with shallow roots, to shade and cool the surface, like Dichondra Silver Falls. A light-colored pot should help.
You never know until you try! This variety is old and not highly bred for flowers. It appears to be Dahlia coccinea. Maybe it’s tougher.
