When you have a heat producing compressor the general rule would be the more air flow and cooler the motor operates the better it is for improving motor life span. I've seen compressor shelters get hot enough to melt the coating on the plug wire plus who knows what else inside the motor; that is obviously why the motor failed. Excess heat build up is generally a problem for all electrical motors and probably electrical circuit boards, including the computer you are using to read this post.
Yeah Bill - In NEMA rated enclosures it's fairly easy to calculate your thermal dissipation requirements, and be it either by convection thru upper vents or the addition of fans or other cooling devices, you can keep it within operating temps. Home made rigs would be much more difficult, so I see where you are coming from.
The Gast 75R looks promising for an enclosure mounted device, as far as utilizing it's fans to suck in and blow out air. Just picked up the leg kit this morning for a Hoffman box I have here. Gast said these can be mounted in any orientation. I'll fill you in later.
