Your bedsides look better than mine did. You can get new angle strips and attach them (spot welding as you mentioned would be best.) Any pieces of the bedsides themselves would best be butt welded in place and metal finished to blend in with the existing metal.
The original board finish was linseed oil with lampblack in it, giving the wood an opaque black finish. What I used on my wood was an oil based black stain that the supplier claimed was good for decks in Fairbanks, Alaska, so should be OK for you in Alberta. It was a very thin material that soaked into the wood, but I did have some issue getting it to dry. I applied multiple thin coats using a spray gun.
This post shows what I used.
Here are a couple pics that'll give you some encouragement (or at least show you what's possible.)
