The trailer I got with mine has a sliding drawbar - basically one piece of box section inside another - you pull out 2 bolts, slide it out and put the bolts in new holes and the trailer is 6ft longer, but I've never used it - its easier to use a beach where I don't need it!
Scaffolding pole is used by somebody else I know here just with a ball hitch on one end and a ball on the other end of about 10ft pole, and a Land Rover wheel hub welded onto the trailer drawbar so when it is dropped off the vehicle it runs back in a straight line. Seemed to work quite well the couple of times I have seen it, but a lot more buggering around than mine.
I'd never put a vehicle in salt water even to the hubs, it murders brakes, the caliper pistons seize up in no time. The most mine gets in is about an inch of water and I only do that when I cock it up...