In car compressor.

Exactly why I am going to install it in the inside rear quarter cavity where the jack sits in my 62 series. Especially because of the heat situation under the bonnet. Also, the bluetongue is fan cooled which is one of the reasons I went for it. As you say, heat kills electric motors. I think I'll ignore the negativecomments I've been given and wire it through a relay.

In 100s I have seen them fitted between the door and the seat. So if you open the rear door it is bolted directly under the seat, surprisingly very much out of the way of everything

Mines quite happy under the bonnet, it's never cut out either, even after doing 4 vehicles non-stop in a row. (16 tyes!).

The blue tounges have a fan cooled motor.

Mine runs while we are driving if using the horns, and personally I don't care for the rattle in the cab while the kids and missus are sitting in there while I'm pumping tyres up, under the seat in a hilux is out of the question anyway, you can barley get your hand under there! Nup, I'm happy with it under the bonnet, and Opposite Lock sell brackets for Under Bonnet mounting, and Thomas build these pumps for air suspension kit's specifically to go under the bonnet, so I don't see the problem. I've hosed it down with the high pressure cleaner and degreaser so many times I've lost count and it's never missed a beat.
It's got a washable air filter on it's intake and it's electronics are sealed, the only thing exposed is the coils for the motor, just like your alternator... Besides mounted where it is, it doesn't see much mud anyway as it's tucked in behind the airbox up high on the wheel arche.

!MPG:13!

I would second the under bonnet installation. Who in their right mind would want the racket of the compressor coming on and off at random ( powering ARB diff locker) inside the cabin?

Electric motors and heat, well, mounting it right above the exhaust manifold is perhaps not a good idea but up front, behind the head light, it runs cool enough.
There is not too much dust there either, unless driving in convoy too close up.
Water ingress? I'd just switch it off during a crossing, there is enough reserve air pressure in my in bull bar air tank to keep the locker happy. Besides, I would chicken out anyway if the water depth was over the top of the wheels ;-)

Klaus

Have a blue tongue MK 1, mounted under the drivers seat and powered via a relay. Been there for over 12 years. Only use it to pump up tyres when I am not driving :-)