If you can source the diamond plate somewhere on your own, a metal roofing company can cut and bend it. They have large power shears and metal brakes for custom forming pieces of sheet steel. Any metal supply shop that does fabrication can also do it and can also supply the DP. I think you'll find it won't cost much to have a shop bend it.
You could always bend it yourself using some say, 2' long pieces x 3/16" angle iron in a vise along with some HD clamps and using a rubber mallet. Slightly bend a section and move it along to the other end and repeat as necessary in small steps to get the required bend angle. By the time you buy the angle iron, it may not save any $$ and if you don't have a vise it's def. best to go to a shop. I made an 18" long bender like the one in the photo for car restoration and crisp & clean bends are possible without having to resort to a metal brake. Not worth the time and expense tho. for a 1 time project.
You might consider using heavier gauge DP to minimize chances of having to do this again some day.
On the white metal trim piece, maybe try asking a local RV repair/parts shop, otherwise a dealer may have it.
Pls post pics when all done...
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