A roof vent is neccessary to exhaust hot air during the summer. The interior temp is kept relatively cool. I chose the Maxxfan because it can be kept open during a rainstorm, so you can still vent, and don’t have to remember to close the vent all the time. In fact, in the summer I leave the vent open all the time, and once I have a solar panel, I will let it be driven directly at low speed after the batteries have received a full charge. I can park in the full sun, leave the fan on low, and when I return it’s not any hotter than the outside temperature.
I only installed one fan in the rear, thinking that may be enough. It’s fine when the windows can be lowered to allow air to circulate. When it’s raining and the windows have to be rolled up, it quickly becomes stuffy, because the air does not circulate. I considered creating a floor vent to pull cool air from under the sprinter, but I’m concerned about fumes, and how to keep out road grime. A vent in the sliding door could work well, but then some louvres on the exterior would be necessary, and likely ugly. The cabin vent fan can be set to run even when the motor is off and key removed, however, it can’t keep up with the volume of the Maxxfan.
The sealant I used is a high quality polyurethane sealant: TremPro 635: http://www.tremcosealants.com/industrial/products/product_detail.asp?id=33
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