Unless you're using direct burial line, then yes I'd use the grey pvc conduit.  DirecTV techs charge 1.25 per foot to trench (2 years ago pricing). That doesn;t include conduit.  I charge my hourly rate + per foot.  

What you described in your post definitely sounds like a line of site issue to me...In my location (midwest) When standing behind the dish, the HD signal is very low and to the right of the dish (that's why you have to skew the dish)....the HD dishes need a very wide berth.  I'd bet dollars to donuts, that they have line of site for 101 satellite, and they don't have line of site for the HD signal..

On top of that, DirecTV only rates their dishes for up to 150ft.  Those technicians are feeding that guy a line of bull.

However, he may just not have line of site and there's nothing you can do about it.

You can easily  check the signal with a satelliite meter (bird dog) befoer you start pulling the lines...I bet it's not there.