I'm envious of your project! I am redoing the inside of a 94 Toyota motorhome and know nothing about wallpaper.
I got lucky and found a guy on the net who is a retired wallpaper hanger and RV'er. He had no issue wallpapering an RV. He suggested using Romans 935 primer, it is used to wall paper over glass and tile and other difficult surfaces. He said he would use a high clay content paste, but was up to me, i opted for pre pasted.
In hindsight I would look for some wider wallpaper, the 21" makes too many seams.
My 2 peso's worth. Plywood can cause some adhesion issues with various adhesives. I always coat plywood with a shellac based primer sealer before I do anything else! Zinsser Bin is a good choice. Jim