On Google Street view there is a picture of a MH just outside the tunnel: http://goo.gl/maps/eVCMd
So, this would suggest you can get through with a MH unless they only came this far for a cup of tea and then turned round! If you swing the view round to look in the other direction notice that long dark, low tunnel. More than a little spooky!
I've only done this area in a car, but some of the D roads were incredibly twisty while climbing. I am not sure how relaxing a drive it will be in a large vehicle. I was freaked by the falling rocks warning signs.
I think it's a case of looking at the map, on paper and inline in fine detail. There should be info online about tunnel heights, although logic tells me who'd build a tunnel at great expense that's too low for coaches/ lorries.
The N roads are not so pretty but might be less stressful.
Thanks guys, some great advice. I did do a 'walk' through using google earth which was fantastic and was the thing that made me nervous! I've changed plan now though and we'll go via Vielha and stop at the lakes etc on the way through if the weather is good. Thanks again!
Exactly the same time as Mrs BB and I did it in 2003 in a four and a half ton Laika and a few times the other way since in other vans. Stopped in St Lary for a few days to catch the market and then up and over. Up from St Lary to the tunnel was a doddle, down required stopping at least three times to cool the brakes. Best spot is the old (deserted) Spanish Customs post where there is some level ground. Tunnel is good France to Spain but a steady climb the other way. If the the Camping Municipal in St Lary has remained the same as it was on our last visit in 2009 it's worth the stop, all facilities at a great price and in late Sept you'll have the place to yourselves. Good luck, it's a brilliant journey.