Keith,
Can't really help on question as such from experience, but if there are holes where there shouldn't be in any air ducting, the efficiency will always be a lot less than one might think for such small holes...
The price of all 3 together seems to be about about 6 or 7 quid, so probably well worth the peace of mind.
Below is a fantastic link for anyone wanting to produce the perfectly insulated and heated air-cooled, relates principally to Bays, but many of the hints, tips, tricks and materials used apply equally to pre '84 a/c T3s too - explore all the links at the bottom of each page if you find it interesting...
http://www.type2.com/library/heat/heat-soundproof.html
The exhaust wrap is now available in the UK from Frosts auto-restorers but not cheap (about £50) and offers a small performance gain due to higher exhaust velocity (only the manifold and not the whole system should be wrapped).
NB. Since this article was written, a lot of cheaper and more easily applied insulation materials have become avaialble, principally aimed at the building trade, either sheet/board products or flexi-wraps for pipes, which may make some of these mods more feasible and affordable.
PS. This great article was 'lost' for a year or two, but was re-discovered in 3rd party site cache and reinstated. As you can see, this guy does not mess about, gutted the van and as good as rebuilt the whole VW cooling and insulation system, learning a lot about VW's half-hearted approach to production engineering a basically good design.
