Read the sticky at the top Underground lines not the place to skimp.
I knew what you meant. I know the arguments as well.posts 99 and 100...
Not the way i would do it.Foam in trench was what i was trying to emphasize.
Anything that is inside a pipe allows water some place to get in and accumulate.
Cost was a big factor where i am,foam in place was very expensive.But losing BTU's to the ground isn't cheap either.