The best solution is a galvanised chassis. There are different brands on the market. Please check which brand has the right homologation (approvals) for your country (for Belgium we recommend Wheels, available at AMIS, Brussels).
If you don’t want to invest in a new chassis, you can reinforce your old one with these parts. These are the same parts as described in the book ‘Ici commence l’aventure’ from Citroën. The pieces can be welded onto an original chassis.
The pieces are in steel, so might have a few 'rust spots'. We cannot treat them because you still need to be able to weld them.