If you have low ceilings in your building use black plastic from the top of the wall to the building ceiling. I know the industry standard says plastic is a no no but our fire inspector is fine with it as long as it is not used to drape across a room where if it melts it would come down on people. When we build pallet walls we use the plastic also to cover the back of the pallets so customers cant see through them.
Instead of using all tongue and groove and having to actually make each panel, how about using a steel u channel sign post, kindorf? It is about $3 - $5 per foot depending on the weight. Put a strip down the top of the wall section and the bottom connecting multiple walls. They make 'L' brackets for them to create bends. I'm not sure if that is cheaper or more expensive than building each panel tongue and groove style, but I am sure it will be much quicker to place a ply wood sheet up and bolt kindorf into the back.
Has anyone every tried this or thought of doing this for their haunt walls?
I know it works and is very sturdy even when barring weight for I have built entire rooms this way layered with 28 seamless monitors creating a complete 360 picture, or 112 individual videos. (It was really cool to play games on hah)