How to catch the plane when the downwash hits it
If you have a bit of wind and a long line it's not usually too much of a problem but if it's dead calm it WILL start to spin when the downwash hits it especially if you are using a larger helicopter.
Two ways that I know of to deal with this:
(1) Fly the airplane right to the spot and touchdown fairly quickly. Basically a "no-hover landing" for the plane.
But if you have to put it on a truck that is tough to do, so;
(2) I tie a 30-40 foot rope to the tail tie down and then tie a heavy shackle to the bottom end of the rope. Position a man on the approach maybe 100 short of the touchdown spot. As you approach come in low enough so the ground crew can catch the rope. It takes surprising little effort to stop the plane from spinning. Now you have all the time you to need to position it nicely on the truck or trailer.
Most of the other stuff about rigging the plane has been covered by others but I cannot stress too much the importance of getting this part right.
FWIW I have done this with helicopters too. Just tie the main blades level otherwise the forward blade will bend down at speed.