Adding another component to the weight list: I removed the upper cabinet above the galley. It was pretty easy to do. Snipped the 2 wires for the single halogen light at the base of the cabinet and installed wire nuts for now. The lights inside the cabinet (on the ceiling) are actually mounted in the finished ceiling of the trailer, so I didn't need to mess with them. This cabinet weighs 28 lbs. I'll install a simple, single wireframe shelf (the look should blend nicely with the existing interior), and I'll affix the range vent/light unit underneath, just as it was on the cabinet. Shelf will be supported at the rear with 4 screws, and at the outermost part of left/right edges (left, screw into closet wall; right, screw into the forward cabinet). Should weigh only several pounds and be very stable. If I change my mind, it can easily go back to original.
Feels a lot roomier without the cabinet.
Just looking down the list at the easy stuff, and estimating weights of the replacement items where applicable (steel spare wheel replaced w/alum; auto jack replaced with manual; etc.) I'm seeing a savings of about 300 lbs. Not bad. As others have mentioned, if it gets too light, the suspension might be too stiff and the trailer would end up bouncing around.
100# (estimated, not weighed) - air conditioner (replace w/Fantastic Fan?)
28# - upper cabinet above galley (includes sliding doors, does not include vent/light unit)
37# - Steel 20# LP tank, full
17# - Steel 20# tank LP, empty
54# - Corner seat at rear (the one with drawer underneath. This includes empty drawer, seat cushion, and 2-piece back cushion.
23# - mattress (replace w/air mattress and/or foam?)
10# - flat panel TV (removed from arm, without arm or stand)
8.5# - subwoofer behind rear corner seat
23.5# - electric jack (replace w/manual jack)
53.5# - spare wheel (steel rim and Goodyear Marathon ST225/75R15 tire) (replace w/alum wheel)