I never had an issue with heat loss. In winter with heater turned on you think you are in an oven as soon the engine is fully warmed up. I'm running a mechanical fan with a thermo clutch.
The only lines I've seen wrapped are the ac lines.
I'm definitely not worried about it in my single cabs lol. I know that life, going from North Dakota winter to getting into a running square it's like a damn sauna. I'm running mechanical clutch fans as well.
Buttttt my suburban has slightly more area to warm up
but then again I do have all of my carpet and headliner ripped out, so that doesn't help one bit, as well as the amount of glass on the truck haha.
SIDE NOTE:
One major thing I've learned though is to make sure your firewall is 100% air tight. There's a few grommets that we're letting air through and it froze my feet for a while before I figured out why it was so cold lol. Once I got those taken care of it was way better. Insulation is also key in the summer, the trans tunnels in these trucks get HOT. So basically if you're having climate control issues, check out these options lol.