Turns out that this welding caper means brackets and fabrication are fairly easy. Lots to learn though, like don’t use that zinc coated massively overpriced product from Mitre 10. Steel & Tube have the good stuff for a fair price.
First cut at front battery box supports is shown here, reusing existing bolt holes. Might have to do it again to make it pretty, but it’s good enough to move on with and takes my weight without complaint.