Insulation: Things to watch out for
The main thing to watch out for with insulation is corrosion - you don't want to be holding any water against the side of the van. Insulation that absorbs and holds moisture is a bad thing, and can accelerate the rusting of your metal from the inside out. And because your insulation is usually concealed behind interior panels, you want to make sure you consider this before you do the job.
First, make sure not to cover up any factory drainage holes. Your vehicle will have drip holes along the bottom of the body panels, to allow naturally-occurring condensation to escape. Products like spray foam block these holes, preventing water from escaping. Many a van has been destroyed by the liberal application of spray foam! Even if you're using stick-on insulation, take care to keep these holes open. It's a good idea to leave the bottom inch or two uncovered, if you're unsure.
Also, consider your insulation material. Cellulose insulation, while environmentally friendly and a good insulator, might not be suited for high-humidity environments like the inside of your van. Living bodies emit a great deal of moisture! Open-celled foam is essentially a giant sponge - not a good idea. Closed-cell foam will not absorb water, so is good on this count (but read more about its drawbacks). Jute or cotton felt does absorb water, but also easily releases it.
Finally, good ventilation is crucial. This isn't covered in-depth on this page, but I'll quickly note that a ventilation fan of some sort is required if sleeping in your van.
This is basically the same issue as above - moisture being retained in your insulation material. Before your van rusts through, it'll start smelling like old socks!
Living in a small space, it's especially important to ensure that your building materials are non-toxic. Plastics, and even some natural materials, can emit toxic vapors into the air, causing anything from mild reactions to severe headaches and nausea. Long-term exposure to some chemicals can have permanent and serious health implications.
Like anything in life, you'll need to come up with your own balance between non-toxic and convenient. Some materials are excellent insulators, easy to install, and cheap - poly-ethylene foam comes to mind (Lobucrud or Prodex). However, they also break down quickly and out-gas toxic chemicals into the air. This guide leans towards health at the expense of convenience, so you'll find some otherwise-excellent insulation materials mentioned but unreviewed for the most part.
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