Hi welshie.
I just went over your previous posts, an I'm sorry I missed the one you posted back in April.
I have no intention of braking your spirit, but I think you didn't need to remove the dashboard.
The air box is meeting the firewall in two places.
On the passenger side there is the cabin air filter, and in the center, the heater core.
Focus on the "heater core removal" document, and I'm sure you will solve your issue.
My guess is that the foam part that covers the heater core, is either torn, or not sealed.
Another option is that the heater core is leaking, but then you whould notice coolant lost.
Do you have A/C in the car, or just heat?