Haven't checked alum lately but, would guess $.40-$.60 per lb. I would guess that a 28' trailer weighs about 5000lbs. I would be surprised if there is 1000 lbs of alum in that total. $.60x1000 = $600. Not much for a 28 footer.
I would use a critical eye and take inventory of the unit. Your climate means to me the outside skin is probably very oxidized. Look at windows for water leaks and broken glass. How many dingers on the outer skin. Where are they by panel and how severe. What condition are the tires, wheels, brakes. Wiring condition? Propane bottles still there? Any type of weight dist hitch? What applicances are there and do they work?
Once I had an initial profile of the unit, I would post on this web site like you are doing and get some feed back from members as to condition and approx. value.
I personally wouldn't want to fight thru the E-bay routine.
Digital pictures are great whether you do them or get someone to take and post a few for you.
28" Amb. deserves better than scrap metal unless it has some major problems. There are folks on this site that would give it TLC and a good home.