I read your explanation downthread that this is only a control line. I
believe that your idea will work, but I would feel more secure installing
1/2" minimum conduit so that you can easily fix any future problems, and
then use ordinary THHN conductors. Sorry, I haven't saved you any money,
but you have

Well, I already have a stock of THHN wire from an auction. And a large
supply of 1/2 PVC pipe. So this route would be VERY cheap. Now, that conduit
will eventually fill with water (all underground runs will). I'm surprised
THHN would be rated for years of water and ice exposure. Is this true????

Karl