TBH, camping with a portaloo is fine, water can be bottled off site easily.
I dare say if there was enough demand a/few portaloo could be rented by Shire for a weekend (though I have no idea how much they are!), and funded as part of the event cost.
Then there's chance if you had more than one site close to one another (thinking about the quarries @nonimouse is talking about) then you camp in between them, and do one site one day, and one the next, in two groups if the attendance is too much for everyone all at once.
There's ways to play this game, I reckon.