In reply to Alex the Alex:
Pretty sure there is no hostel in the Uig area, it'll be either camp at Riof beach campsite (the aforementioned, it's not too bad really, but better to wild camp somewhere else imho). Nearest hostel accommodation that I know of is at the Blackhouse Village
http://www.gearrannan.com/hostel.html
Other than that it's Stornoway at the HebHostel, or Scaladale Centre on the way to Tarbert if they don't have groups in. Might be worth having a nose through the community shop website, they have some self catering links on it and a contact page. It's pretty much the hub of the community over there, so if anyone knows then they will!
http://www.uigcommunityshop.co.uk/index.php/isle-of-lewis/38-tourist-inform...
Isi