.
Oh Jeez, is it time for the cooler-in-the-wheel-well thread again? Seems like just yesterday...
Yeah, Gordon is pretty much on top of it, as usual. With 8x10 color glossy photos and a paragraph on the back of each one.
Yes, the stone guard is important. And no, none of the coolers comes with one, so you have to fabricate something on your own.
For years, Vintage and a few others mounted coolers in that closed space between the engine compartment and the rear seat/shelf because it's the most convenient spot for a builder. It's a wide, flat panel close to the engine (short oil line runs) and you can route the lines there without interfering with the exhaust or valve covers. (It's also protected from road debris, so you don't have to fabricate a stone guard.)
But, it's not the best place in terms of efficiently dissipating heat. And the main point of having an oil cooler is to, well, dissipate heat. So, VW folklore has always said to mount them in the wheel well.
But now, Greg at VMC is putting his in that compartment again, flying in the face of folklore. I'm guessing he gets away with this because he's standardized on a Pat Downs build that's in a mild state of tune and with very cool-running heads. (And maybe some other cooling tricks he's keeping close to the vest.)
If your engine is in a higher state of tune and you're already close to having overheating issues on hot days, I'd definitely put the cooler in the wheel well. But, as noted, routing the oil lines around the exhaust headers will be a challenge. Not impossible, but a challenge.
My wheel well mounted (Setrab) cooler has been doing the job without a hitch for about 10 years, now. I'm in California's central valley where most summer days are close to 100, and the fan-assisted cooler isn't an option, it's a necessity. You can watch the oil temp drop back to the center of the gauge when the fan comes on.
The car came from Vintage (in 2013) with a lesser cooler mounted in that space just behind the seat/shelf and the engine would routinely overheat with it mounted there.
This is, of course, free, unsolicited advice, so you'll have to draw your own conclusions about its merits and relative worth.
.