In case someone else needs this info... I had a meeting with the MOT inspector today, who says that if I grind back the plate as much as possible, cut a new flat plate, and weld it over the top of where there old one was, and weld the top and bottom joints it'll be fine and will pass the MOT no problem. That's my task for the weekend. It's 3mm thick steel so I'll need to practice as I'm used to welding thinner steel.
Mine was really bad so I made some plates. I cut out all the rust and welded these over good metal. And yes make sure to use seam sealer. Mine was all cracked and figured the salt/water got behind this and ate it away
Looks like you and I did exactly the same thing although I seam welded the plate. Only one side was needed. I used lots of seam sealant and 121 epoxy restoration mastic. The small section of floor just above the strut eye was so flaky I had to clean it all back and cover it with some steel plate. I couldn't get a weld in, but used some plastic, then galvanized steel plate, epoxy mastic and seam sealant. Solid!
Thanks for replying! And sorry I missed and isn't respond