If your putting it on a pole and dont mind what it looks like a standard £10 house ariel will do the job, and arguably better than any of the units designed for caravans.
If you want it to go on top of the van go for a decent directional unit, it's worth the extra money. The omni directional units generally round in shape are not as good as directional.
I have one of these http://www.maplin.co.uk/12-24v-outdoor-digital-aerial-476170 I am currently in an area that has really bad tv signal even the houses around here have to have boosters or communal aerials yet I'm still getting most of the digital freeview stations, can't even get a satalite signal so I would say it is an excellent little aerial and I would say a lot better than any of the standard array roof of mounted caravan aerials.
------------- here today , where tomorrow?
yet another full timer,
Quote: Originally posted by the warbies on 05/5/2013
over tightened the screw on roof mounted ariel any advice on how to loosen
You might have to push on the screw whilst unscrewing. Someone will be along soon to give further advice. I only know that when screws are over tightened, you can usually get them out again simply by pushing on them whilst gently unscrewing at the same time that you push on them.