Very many thanks Vernon, we are going to Christchurch so will take your advice and use the A466 and A4136. Just hope now that we have some better weather!!
Alun
I live in Chepstow; I'm sure you'll find the A466 no problems with regards to towing a caravan. You're right in thinking that it's a bendy road, but it's wide (over the past few years it's been widened).
A good place for a quick break-stop would be the left turn just BEFORE the Abbey Hotel; just as you approach Tintern. It's a big car park (up a slight incline), and always has loads of parking; easy to get a caravan in and out.
Remember it's the turning just BEFORE the entrance to the Abbey Hotel (it's not signposted as parking). It's almost opposite the Tintern Abbey.
Oh, while you're in the Fod, make sure you visit Clearwell Caves; it'd be worth the effort.
Regards.