After selling my previous yellow WR17, realizing the error of my ways and buying another, I had to come up with another compass mount. So there are two versions shown below.
These are just compass mounts, but as you will see, you could use it to mount just about anything to your cross-tubes. Simple. Cheap.

Here is the first step. Cut a 3 inch diameter slice of PVC pipe and then take out about a 45 degree section of the total diameter.
Drill a hole at the point where you will mount the item.
Make sure to figure on how much the rotation will be around the tube. You may want to have one or both ends rest on the hull.
Countersink the hole so that a "V" shaped screw will sit below the interior surface of the PVC. I
chose nylon to avoid the risk of scratching the aluminum cross-tube
(even though in theory, it was countersunk enough to sit off
the tube).
I used two of these rings on my original compass. This is shown below, as well as another arrangement that I am using with the new WR. The new one also has a rubber pad glued underneath in order to keep it from slipping on the aka tube.