I haven't given up on this yet. My blower started making a horrible noise the other day, so used it as an excuse to buy a 270cfm 4" blower to test with the heater. At $70 I would be happy using two of these if need be. Will now have to dig out a battery and see what the flow is like through the core. All going well, I will build a proper box out of alloy next and mount two of these suckers on it for lots of hot goodness.
Will then need to work out how to make some hot tubes on the cheap. Thinking round car vents and some tricky alloy tubing with flexible inserts etc.