Plastic is preferred. My question is why is your secondary pan filling up with water? The air handler drain pan has a primary drain and a secondary outlet. When the primary drain is clogged the water level rises and comes out of the secondary drain. I have installed float safety switches on the secondary outlet to shut off the unit and prevent water damage to the area. If this pan is a secondary, have your problem fixed first. Grainger does not do on site work.

Their web site, or google the model number for parts.

Your options are limited. A portable 12,000 btu unit runs off 120 volts and needs a 6 inch hole for the heat exhaust duct to vent outside. They run about $500.

a water treatment like the one you mentioned or an additive that contains a lubricant for the seals and bearings. It also helps keep down oxidation on internal parts. Either is available at johnstone supply or maybe grainger