eye watering pricing. The Wickes near me have one too. Luckily the bathroom displays are right next to it so you can collapse into a seating position on one of the bogs when you see the price lables.
The smallest BMS angle seems to be 3mm thick. If you need thinner, you can get 20 x 10 x 1.5 box and nearly cut it from that, 20 x 20 would be better, but it will have a good radius on the corner. For short sections, another option is to mill from solid out of 10mm square bar.
Then some fine fibreglass mesh after a bit of sewing, still looking for some reasonably strong flexible magnetic strip.
I have had to use some little magnets in the mean time. Once the council tip opens back up I should be able to get some strips from an old fridge door.
Fitted.
Tested!
It didn't make any difference to the running temp of the car too.