Thoughts on the RS3 mate?
I'm running them on my car at the moment, I've found them to be very hard. Cope well with more laps/hotter days but take ages to get any heat into them.
You'd be surprised how common the leak I mentioned above is, not visible unless the car is up to temp and running, even then it can still be hard to spot.
Very common problem is a leak around the join where the end tank meets the radiator core. It will only leak once up to temp/under pressure, so if you turn the car off and try find a leak, you won't.
Look for steam or drops of water staining around the top radiator hose or generally around the...
You can cable tie it to your ABS module or anything like that, also to your battery clamp (thing that holds it down)
Or you could cut out a piece of MDF or similar and mount it on that in the engine bay, lots of ways.
Here is a messy example