If 3-4 months advertising for Thunderground - including full page advert in Classic Rock and 2 other smaller ones, as well as lots of exposure on mr.com - to see such a great line-up for only £22 sold only around 300 tickets, then Wig Wam + Dante Fox, being promoted for a week, will NOT sell out a 480 capacity venue. So I wouldn't worry about not being able to get in.
And people stating about losing money on hotel rooms ... surely most hotels have a refund policy if cancelled more than 1-2 days in advance (this is usual policy of all hotels we've used for Gods or Firefest festivals).

So if you're thinking of going to this show, GO! You should have no problem getting in.