Heat too. Triples have a LOT of heat focused in one area. Although with a Duramax you have the secondary sitting in the middle, where on my Dodge all three are in one place, so may not be as much of an issue on your truck?
The space and heat were things not mentioned to me (or I just didn't listen) when I got mine. I mean I knew about the space, but didn't think about the SPACE and how things were routed and such.
I've battled melted AC lines, melted wires, and melted coolant lines. Again, on a Dodge and not a GM so may very well be different/non-issue.
Mine have Levi's blankets on all 3 turbine housings and the complete hotpipe. Heat isn't a problem. Blankets should be part of any compound setup.