Buy some 99% proof isopropyl alcohol IPA. Get it from eBay. Great value. https://www.ebay.co.uk/itm/IPA-99-9-1-LITRE-Lab-Grade-Isopropyl-Alcohol-Isopropanol-1L/141522873981?epid=27031978691&hash=item20f36bae7d:g:ACEAAOSwzrxUsbES
It is a matter of choice but my advice is don't bother. Lay the track straight on the ply. Just paint the ply first, both sides and all edges. Any old emulsion paint will do.