Instead of plastic I use either plant derived cellophane for wrapping my soaps. Alternatively I recycle the see-through wrappers you get on birthday cards.
Melt & pour soaps need a wrapping because the glycerin they contain attracts moisture from the air which causes small water droplets to form on the surface of the soap – so-called soap ‘sweating’. This is not an alarming phenomenon, as it is natural for the glycerine to attract moisture from the air.