Kombi Battery Area Rusted Out

Hi All.
The floor of the battery compartment has rusted out, so I've transferred the battery to the other side (the near side) and run a very heavy cable across. It now sits in a stainless steel tray, on non-slip matting, and doesn't move, touch wood.
The rust, however, hasn't stopped and is eating through the rear of the Kombi on the offside rear, below the tailight. What to do? Have someone weld in a small panel?
Replace the corner (quarter?) piece?
Perhaps I didn't use enough baking soda to neutralise any spilt acid? Any suitable repair shops in the Melbourne, Ferntree Gully area that you can recommend?
Thanks. Paul.

Give it a good helping of rust converter (Rainex Ferrepro ect) and then fish oil. That will slow it down untill you can afford to have it cut out and new metal welded in, the sooner the better!
Rob..😎

Righto. Rust converter, good idea. Will do it this weekend. Thankyou.