Just us 25 x 3 flat for the strips. You can use stainless if you want or use galvanised mild steel or just paint. The outside end will have to be curved a bit to follow the curve on the end of the timber.
Cut your ply to size first and mark on it where you want the strips to sit and then lay the steel on these marks. Mark the steel to length and cut. Drill a hole and csk where the strips cross each rib.
I didn't use marine ply in the van as it's out of the weather, just cheap stuff and gave it a coat of laquer.
I went to a bit more trouble with mine and got the ply routed so the strips are recessed into the ply a bit but still sits proud of the ply.
I used stainless strips and polished them. I have the originals and they are not stainless.
If you want some photos send me an email and I will send you some.
gcran@westnet.com.auGraham