It surprises me to hear about the variation in the seat temps. On other forums and here it seems like some get too hot and others not hot enough. Mine are underneath the padding instead of in it so it makes sense mine wouldn't get warm enough without doing this mod.
Anyway, glad to hear this will help your back, cakM3!
2005 BMW 330i ZHP 6MT. Built 11-19-04. Bought 4-2012.
Stock: Nav, leather, PDC, Xenon
Added by me: OEM Alarm, OEM heated seats, OEM aux kit, OEM Bluetooth, intravee, M3 strut brace, BMW Performance Intake, Nappa leather arm rest, updated LCM (triple blink, euro hazards, trifecta lighting, 3 stage brakes), temp gauge