My RTV had a heat problem from day one that would cause it to shut down after a few hours' operation. I was already addicted to my RTV and didn't want to return it, and I also didn't want to void the warranty by opening the box. The obvious answer was to add an external fan.
To do this, I cut a hole in the center of a black plastic tray that was the same size as the outlet of a 12 volt DC fan. I then mounted the fan on the inside of the tray so that the fan blew air out the bottom. I powered the fan with a 6 volt wall-wart (observe polarity). I placed the tray upside-down on top of the RTV so that it acts as a plenum that covers 70% or so of the vent holes in the top of the box. Now my RTV runs about 30 degrees F cooler, and the warranty is still intact.
The 12 volt fan runs very quietly at 6 volts, the black tray is unobtrusive, and there are no mods to the RTV at all.
If you are concerned about dust, you could orient the fan to draw air into the plenum and place a filter on the intake. If you do this, you should use a larger tray that will cover more of the vent holes in the top of the RTV. Using this orientation, the interior of the RTV will be pressurized with cool filtered air.
To do this, I cut a hole in the center of a black plastic tray that was the same size as the outlet of a 12 volt DC fan.
This is a great idea for quick and dirty cooling until you get a chance to mount the fan inside. You might want to tape down the tray to the top of the RTV to keep it from moving off. You may want to consider a fan guard to avoid possibility of finger injury by friends and family.
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