I don't actually have an outfitter, but I also have a double jet ski trailer converted to carry 2 Pro Anglers. I got several confusing dimensions when I inquired, so what I did was lay the 2 pieces of 2" PVC loose on the trailer, then lay the boat on top of them and let it tell me how wide it wanted them. With the boat settled on top of the PVC, just mark the trailer boards where you want them, remove the boat, and install the bolts to hold the PVC. This should do nicely.
Finally Retired, Fish Beware!
2013 Hobie Pro Angler 14
2012 Hobie Pro Angler 12
2001 Hobie Hank Parker Edition Outback