We use a mix of starch and ‘artists choice’ plastic varnish (dubbed barrier starch) to seal the backs of any translucencies that need to not bleed through. That will keep even liquidy faux dye from seeping through if sealed correctly. We usually use 3 coats of the above mix on the back, then flip and seal the other side twice (which you could probably skip), but keep in mind we almost exclusively work on muslin.
Adding any plastic type sealer to your size may give you what you need as long as you keep the size/sealer itself from soaking through to the side that you want as a painting surface. This is where several light coats would be better than fewer heavier coats. Good luck!