This is just merely an example:
If I built an exchanger for a snow machine I would make all lines very straight with exact bends.
I had a customer ask me to get their in floor heat hooked up to their wood furnace about a month ago and I made this exchanger to extract heat out of it. This furnace was not designed from the factory to incorporate any sort of an exchanger, so it was a PITA! Mostly due to tight working conditions. Started with 3/4 copper and t-drilled into side and capped at each end. Made several loops of 3/8, ended up with about 50ft total inside. When a good hot fire was going coolant going in was about 80 degrees (return from floor) and 130 degrees coming right out of wood furnace (supply to floor).
If a guy were to make a cooler using similar principle of the one in the pics it should work very well. There is a 13'' by 60'' rectangle of room between the two coolers which run all the way down tunnel, then from front bulk head cooler to back cooler on a 162'' m. I estimated tonight looking under mine (skid is out) that I could fit 8-9 loops (about 9-10 ft per loop) above the track. Cooler would be really low pro, only about a total of a 1/2'' tall. This would include sections of flattened out 1/2'' I.D. copper that would be brazed to all 3/8 O.D. running perpendicular to them. You would drill through these flattened pieces and rivet the whole exchanger in the tunnel as one piece. So all in all a guy could have from roughly 72-90ft of exposed exchanger above track in tunnel! There is really no way this would not produce super cold liquid temps right before inner cooler. The only times the loops would be perpendicular to track would be at very front right close to front cooler, there is a decent void there anyway when track goes around drivers, and at very rear just in front of factory rear cooler, there is always a big gap due to tunnel tipping up after rear suspension drop brackets. It is lower pro than factory coolers anyway. Copper should be more resilient than factory aluminum coolers too, copper can dent quite a ways before it will split, if a rock or something hit it, unlike aluminum. If a loop got smashed flat for some reason coolant would still have many others to flow through. Everything would need to be brazed, not soldered. I am talking about soft copper (comes in a roll of 60-100ft usually), not straight sticks of 10-20ft.
Snowest seams to have a problem with getting images uploaded tonight so I will try editing this post tomorrow and put the pic of the wood furnace exchanger up, it will help you see kind of what I'm talking about.
(12.7 to 11.8) It seams worse in cold weather
I am going to try restricting the flow of coolant though, hopefully it will heat up faster but stay cooler. 
field low elevation. 
