...better part of a 50’ roll of heater hose running along the frame to the heat exchanger mounted up high where the spare tire used to be. I used a 2.5 Gallon air tank, a B&M tranny cooler with ¾” hose fittings with Spal fan. Works very well. I often check temps with an IR Gun and the intake air seems to stay around 20 degrees over ambient, sometimes a little less. The run to the tank and back is long enough the fan has never come on and it has a sensor set at 120. That said, I'm in Phoenix and rarely wheel when it's much over 100 outside.
This is really interesting - WE WANT PHOTOS!
An advantage of the remote heat exchanger location is to completely de-couple the heat output of this one from the other ones already in the system.
Plus, the obvious one - no mods up front.
So - no pre-heating of ambient air entering the A/C condenser / engine coolant radiator, that is already taxed near it's limits.
(arguably, ad nauseum, this radiator, that radiator, pusher fans, bah, blah. Please, let's NOT

again here!)
The point is - you don't bother it.
It seems that what you are saying is that the length of tubing itself, round trip all the way to the back, is enough of a heat exchanger to be effective.
Hmmm. OK, in that case, how about somewhat large diameter aluminum tubing, back and forth along both frame rails.
Fill any available underbody area with tubing.
Zig-zag where you can.
Jump over inconvenient routing locations with ordinary rubber heater hose.
It's a low pressure, low temperature system.
An upgrade - Half flatten/ripple the tubing to increase flow turbulence to increase heat exchanger efficiency.
- Low cost.
- DIY.
- Rugged.
- No fan.