We are using wood. It is what we are very comfortable with using (and we sold the welder a while back... can you see them allowing us to run a welder in a campground???). Some partition walls are trimmed down flush lauan interior doors
(runs roughly $1 per inch in width). Same price or cheaper than building similar wall from scratch. The shower wall with the plumbing inside it will be built from scratch as we need to accommodate the plumbing for the shower and the washing machine. We screwed a length of ripped down 2X4 (to fit flush with the metal angle the seats bolted into)) to the sidewalls with drywall screws and attached the doors to the wood with drywall screws. We used a small "L" bracket to secure the front to the partition to the ceiling/floor. We positioned the L brackets to where they will be covered with cabinets to be installed later.
This is one of our bathroom "partition" walls. We used a 28" lauan door. Only one side is painted. The unpainted side will be "in" a storage closet.
This bracket (front of the partition, on the ceiling) will be hidden inside a closet
the wood strip we cut and attached to the sidewall to attach the "wall" to.
back side of the vintage medicine cabinet we used. we put the wood strips in the attach the medicine cabinet to. not much to attach anything to with a hollow core door. All this will be inside the closet. the medicine cabinet had an arched top door. But we had to flip the whole deal over because the curve of the roof prevented us from opening the cabinet.