""I seriously considered doing stainless but couldn't bear thinking about how much heat they give off""
That's a popular myth but the opposite is true. Between mild steel and stainless the stainless transfers heat about 1/3 as much as mild steel.
You will get a reduction in heat transfer with coated mild steel but I'm not sure if it's as much as 1/3 of uncoated.
Coefficient of Thermal Conductivity BTU/ft-hr-F( 70 F )
Aluminum 6061-T6----- 96.50
Mild Steel 1010 CREW----- 26.98
304 Stainless Annealed ASTM A269----- 9.40 TECH ARTICLE