I'm sure every area has their own rules on the spacing of underground utilities. Here you have to have undesterbed soil between your lines. They are not allowed in the same trench, but there is no distance requirement.
The reasoning has to do with being able to get to one without hitting the other. Just imagine having to dig up your water line if it breaks and hitting your electrical line with the trench full of water.
An undesterbed barrier has a certain level, or ability, to retain water if it breaks.
Why are you using black poly? That's a huge line your running and that stuff is prone to break allot more frequently than Schedule 40 pipe. The water companies around here used it years ago, but realized it was a huge mistake and don't anymore. They have to keep a crew on the road 24/7 repairing breaks in the line. When it happenend to me at a house I used to own, they told me they had already repaired several that day and had more to do!!!
You can only hang 4ft off the back of a truck bed or trailer, and you need a red flag when your that far out. How much material are you buying? For small quantities, I've tied stuff to the top of my cab, or with 20 ft lengths of PVC pipe, I've tied them to my mirror on the side if I only needed one or two pieces.
Of course, now I have a 16ft trailer, so it's all taken care of with that. If you don't have a trailer and are buying a bunch of lumber, I'd have it delivered.
When I bought the metal for my roof, I had one length that needed to be 32 ft long. Cost $75 for delivery, which I thought was a bargain. They brought all the material and had a forklift to put it exactly where I wanted it.
My lumber yard will diliver for free if I spend $500. Have you checked to see at what point delivery is included? It doesn't take much to get up to $500.
Eddie