Just spent Easter building this and I'm pleased with the result. I set a very small budget of $500 as this is not something I'll use daily but it's already done a couple of trips and it's been brilliant to have along. I blogged the build here:
http://4wdx.com/a-functional-expedition-trailer-for-under-500-can-it-be-done/
and here I installed on-board water:
http://4wdx.com/on-board-water-tank-for-the-expedition-trailer/
http://4wdx.com/a-functional-expedition-trailer-for-under-500-can-it-be-done/
and here I installed on-board water:
http://4wdx.com/on-board-water-tank-for-the-expedition-trailer/