The use of insulation in custom vans that will be used only in warmer weather is a hotly debated topic. The answer depends to some extent on your van’s setup, your budget, and the amount of effort you’d like to put in, but we’ll discuss a few of the key points.
To put it simply, insulation will slow down temperature transfer, but will not stop or reverse it. This means that an insulated van’s interior may take longer to reach the same temperature as the outside air (and stay cooler for longer), but it will also take longer to cool down once the outside air temperature is lower. If you're going to be living entirely in a hot climate, in many cases comprehensively insulating a van as many guides would traditionally suggest will be pointless or not worth the effort from a temperature perspective (keep in mind there are additional benefits of insulation such as noise reduction). Many people living only in hot climates go with limited insulation in the walls and ceiling, or even none at all - but if you plan to have any exposure to the cold, it’s worth re-evaluating.
If your van is on the more basic side, and doesn’t have an advanced electrical system, it’s unlikely extensive insulation is going to be the best route to keeping you cool. If your system has the ability to incorporate serious ventilation, you may have more control over the delay of temperature transfer (ex. by forcing hot interior air out of the van quickly once the exterior air is cooler). Essentially, the decision to insulate or not in hot climate comes down to your setup. When coupling this factor with the budget required for insulation and the time to install, many vanlifers that only live in extremely hot climates choose to forgo comprehensive and traditional insulation.
A few things to consider about vanlife in hot climates and insulation:
Far and away the most important thing you should focus on, which will make more of a difference than insulation in exclusively hot climates, is parking in the shade, covering up your windows and creating air flow.
For effective ventilation, at least two openings are needed - one for air to come in, and another for air to exit. Often, people will ensure these openings are on opposite ends of the vehicle to allow for maximum length of draw throughout the van. Ventilation may come through the form of windows, open doors, and fans - the latter will help to provide optimal ventilation, especially when multiple are used in varying locations throughout the vehicle.
Direct sunlight radiation via the windows will substantially contribute to the interior heating, so reflective sunshades should always be used to protect open glass areas. Some people also install darker tints on their windows, or design custom homemade window covers (ex. With Reflectix on one side) for extra protection.
Availability of shade is going to be dependent on your location and travels, but many people will create shade when otherwise available through awnings, tarps, and appended platforms to the top of their van.
If there are particular areas of your build with high conduction potential - meaning exposure to really hot surfaces/items (think your batteries, the engine or exhaust through the floor) - consider a heat shield or insulation to protect these particular areas.
For example, floor insulation can be worthwhile due to convection and radiation as a result of the heat generated from the exhaust and vehicle mechanics under-mounted. Similarly, if you’re parked on hot surfaces like black pavement in the summer, floor insulation may provide a necessary barrier against conduction. You would use standard materials for insulation based on the highest potential R-value.
Where can I find first-hand answers about insulating a van for hot climates?
Reddit is a great start:
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