+1 on Thermoliner. Like Chris152 I also spent ages researching various ways to insulate my camper conversion. And like him I also found that the best stuff was Thermoliner from Harrison Trim Supplies. But I suppose the whole thing is moot until you decide how far you want to take it/how much you care. Ha ha. I choose Thermoliner because as well as insulating, it also has very good sound proofing/sound deadening properties. That was really important because my van (a 2001 LDV Convoy) is VERY NOISY. So I didn't scrimp on trying to make it a bit quieter (you can't hear music whilst driving it's that loud).
I also chose it because it won't trap as much moisture as loft insulation or other similar products (I looked at both natural and synthetic insulations). It's also its own vapour barrier which is good, less work to do. I learnt over the summer while sleeping in the camper for a few weeks that moisture really builds up, so I think I made the right choice.
Like Chris said, it's easy to apply (especially when used with a heat gun) and the adhesive is good. It cuts easily and all these things add up to less time spent actually faffing about insulting your van, which isn't exactly the most fun activity in the world. It is more expensive than other insulations but for a Caddy it shouldn't be too bad.
Having said all that, if you've got some leftover insulation and you're happy with what it then go for that! It will provide some noise reduction but not a huge amount.
Not trying to give a hard sell but I distinctly remember how boring the whole thing was to decide which to use so hopefully it's of some help.
