Many thanks guys, thanks for the info. I lost track of this thread.
Elvis, I visited an acoustic specialists and got some prices. With the soundproofing membrane and then the insulation it suddenly became a sizable amount
I take your point about the soundproofing not being needed all over - i was wondering how much would be optimal + I am also planning on floor areas.
Then I was looking at the silver sided foam (like used in engine bays) and figured that anything stuck to the walls would stop the re-verb and act as soundproofing and if its the insulation then bonus - could this remove the need to have soundproofing membrane on the side walls? I'm thinking yes.
I would stick a couple of large squares of the soundproofing membrane on the roof to kill the vibration and then have egg box type foam covering every inch as its much lighter and less likely to interfere with the roof lining.
I hadnt planned on completely filling the cavity between skin and cards this time! I thought having stuff stuck to inside of skin and stuff stuck to back of card panels would kill the noise, it would insulate enough yet remove any doubt of moisture trap. Will read up on this but I think allowing circulation would remove moisture and insulation would be suffiently effective
I dont know how much benefit there is from insulation anyway! when its hot - its still bloomin hot in the van and when its cold its brrr. I spent a small fortune on stuff to do my T5 and it didnt miraculously create a micro-climate.
As I will have an erber in the T3 I can get warm if I need to and accept there will be heat loss, I will still revert to opening a window when its hot. Killing the noise is more important.
If I had double glazed windows on the van then maybe insulation has more bearing, I just dont think the cost is justified unless someone can educate me otherwise.