Broom sticks with the right sized screw in them can make cheap monopods. They dont rust either. Try some of the Ti and wierd alloy ones that are around if you want to spend some bucks or ask Leigh Bishop what he uses on his long exposure shots. Manfrotto do an alloy mono that has a removable base the turns into a supported mono. Wouldnt be fully as stable as a tri but its a lot more compact. Not sure about the rust and corrosion issues but there are a few different metals in them.

Matt