Time for an update on this. I bought some steel square section off eBay and some sheet plate. Pure serendipity as a few days later my electrician popped round for a chat and a coffee and it turns out that he's a keen metalworker and got a lot of kit. So he helped me cut the tube squarely to length and then welded a couple of studs onto the two end plates to help hold them and the square section together while I fitted them after being chromed up.
I came to the conclusion that I didn't need to weld those endplates on as the welds would never be as clean and crisp.
Yesterday I collected them from the chrome guys who have done a fantastic job.
If I get time later today I'll fit it
If opportunity doesn't knock, build a door.