We have ovens for 60lb. rolls of wire, but that would be a bit pricey for your application. Since you are not using large quanities, I believe I would be tempted to use an old dorm room refridgerator with a 100watt light bulb. Something to mainly keep the wire dry and clean. Something heated, because it might tend to sweat with temp. changes, if not heated.
Post a request in the "Equipment Wanted" section for a used "adjustable" rod oven that you could turn the heat down (to keep your plastic spools from melting). Maybe someone will have one cheap.
Give it try, can't hurt anything to ask,
John Wright