I'm thinking aboout something reasonably transportable that will fit into the back of a 4X4 in one go. It would get moved three or four times a year rotating between specific spots so semi permenant footpads of some kind could be rigged up quite easily with perhaps a deep driven central stake to attach a centrally suspended anchor line to. A lean-to one would do at a pinch but its a bit restrictive. There's one I use which is only about fifteen feet high and its fixed to a scots pine. When the wind blows I either fall asleep in it or get seasick.
Mereside, out of interest, how much would a thing like that cost?