Hey Hog, be sure to place them where you can relocate them easily as they don't show up well on a depthfinder. I won't ever put them out on a large flat anymore. I've got a few that I've never found again since I put them out.
I use a Garmin Etrex Camo GPS but it is not WAAS inabled. The accuracy is only guaranteed to 100 feet.
When I put more PVC attractors out I am going to place them along the breakline of the creek or river channel edges. This way I'll drop a bouy when the GPS says I'm close then I'll mark the channel edge 20 yards or so to each side. Then I should be able to locate the PVC by fishing back and forth between the bouys.
Even though you probably won't see the PVC on your graph and you probably won't hang up on it you should feel your line sliding over the pipes and you will most likely catch a fish when you contact the bed.
Good Luck!
CATCH A BIG-UN