I need some help with my first package unit install. It is a 20 year old lenox 3 ton system. Can you guys give me some tips on small things,(Wire size from disconnect,Ducting size and # of vents).By the way this is a 1200 sq ft trailer and the ducting will be ran under the floor. I know this isnt the most practical way to do it but it was a 200 doller unit for my friend that needs a/c in arizona. Can you guys give me some info on stuff need for a first install.(Tape, flex duct, steel duct.) I'm also on a 250 doller budget for supplies.

Thank you