I know there isn't as much clearance as the owner manual states so I don't know what the long term problems may be, but I don't think it's going to be a problem. Here's what I think:
Running the fridge in an enclosed space will cause increased heat which may make the compressor work harder. If the compressor works harder, it could potentially shorten its life.
In the RV, the fridge is not on all the time, only when we are actually camped. During the day when I'm outside the RV, I open the outdoor kitchen. Any excessive heat is easily dissipated on the open air.
At night when I close the outdoor kitchen, the fridge may operate at a higher temperature, but it's only for a short time and I don't see it as any different than if I was living in the deep south and the fridge was inside a house or cabin running 24hrs a day in 90-100 degree weather.
We're not full-timers so our outdoor fridge gets much less use (even at less than optimal conditions) than it would being used inside a house like it was designed to be. So I use it without worry
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