The next stage in my little project was going to have to be insulation (well it could have been windows but I was still plucking up the courage and waiting for a break in the weather). As I mentioned earlier the aim was to make the van habitable all year round and with no plans to fit any heating this was going to require a good level of insulation. Prior to making a start though there were a few little jobs that needed some thought before the metal work got covered up. This is where and why it helps to have a good idea of what the finished article is going to be and a good plan of how to get there, if the plans rubbish you often end up having to rework parts or changing the design to rectify things you've missed.
As such I took the opportunity to fit a couple of earth studs in areas where future electrical items were going to be fitted and pulled through the cables for the leisure battery charging and lighting circuits. I also fitted a series of RivNuts (threaded blind rivets) into the roof area ready to bolt the roof lining too, I could have just used self tapping screws but there was already a set of nicely spaced holes provided by Mr Vauxhall that seemed too good an opportunity to waste.
It was then time to consider how best to insulate. Looking at various websites, it seems that there is no right or wrong and everyone's got a different idea. In the end I went with a 3 layer approach, consisting of: 1) A layer of Silver Foil Insulation glued directly to the cleaned and de-greased van skin, using High Temp spray adhesive. This is allegedly the equivalent of 55mm of polystyrene and has a R value of up to 1.455 m²K/W whatever that means. 2) A layer of Recycled Plastic Insulation with extra stuffed into all the little nooks and crannies. Apparently being made of plastic this shouldn't, in theory, absorb any moisture should any get in there, and has an R value of 2.27 m²K/W. 3) Another layer of Silver Foil Insulation again fully glued to all surfaces and finally taped, to provide a fully sealed vapor barrier, in theory, sealing the van interior from the external surfaces and preventing any moisture from inside getting to the van skin and outer insulation layers (and vice versa).
Whilst this wasn't the cheapest approach, and most of the research I did seemed to point to most people only using a single layer of one of the materials above, I'm hoping that the additional cost and time will pay off in the future. In the end I used about 1 and 1/4 rolls of the Silver Foil Insulation, with the remainder of the second roll being used for the floor, 5 rolls of Recycled Plastic Insulation and about a 10 cans of High Temp spray adhesive so not cheap but not stupid money either.
When it came to the floor I felt that the same approach would result in too thick a floor and loss of valuable head space, it wasn't a problem with the roof, as the insulation was helpfully about the same thickness as the roof beams which the Ply lining bolts onto, so resulted in no loss of head room.
With the floor I opted to bond thin wooden strips (laths) directly to the van floor to give something to screw the new floor down to without having to penetrate the van floor. This resulted in a gap of about 10mm between the top of the wood and the van floor, into which I glued 2 layers of the Silver Foil Insulation cutting it to fit between the wooden strips. As with the walls etc this was followed by a further full sheet of Silver Foil Insulation covering the entire floor, which again acts as a vapor barrier, with the Plywood floor screwed straight through the lot direct to the wooden laths.
Whilst there were no problems with fitting the insulating layers, it was incredibly time consuming. The biggest problem was cutting the middle layer to size, because its quite tough and pretty thick it required numerous passes with the biggest pair of scissors I owned to get through it. I think that if I had to do it again, and I see no reason why I won't, then some form of guillotine may be a better method, I'm thinking of the sort they had at school when I was a kid with the big blade slicing against a metal edge (perfect for losing fingers).
It was quickly apparent as I worked and built up the layers that this approach is quite effective, not only could I feel the internal temperature increase as the layers built up but the van went from being an echo'y hollow space, to feeling quite solid and the doors now shut with a reassuring thud instead of a tinny clang.
Having been finished for a while now I can confirm that this approach seems to have been effective. I've now been out on nights with the temperature well below zero and whilst it was chilly, wrapped up well in a sleeping bag, it was plenty warm enough and as soon as the kettle was on in the morning toasty and warm. Likewise in the summer the temperatures been up to 30 and once the skylights open and the stuffy air let out it was never overly hot, so it seems my plans worked out and the extra effort was well worth it.