Snoman,

to the forums. If you looking into a rod rack, we have some photos in the float tubing rigging section of a few different racks. For a homemade rod holder per sey for your active rod while trolling, I have only seen one made. It was out of PVC like Fishyaker said. It was made from 3 pieces of PVC. The longer piece (about 2 foot) was joined to a 45 degree angle, which was joined to a piece about 1 foot long. He used straps to secure the 2 foot piece to the top of his float tube and used the 1 foot piece to slide to rods into to actually hold it. It worked for him trolling for trout, but he was limited in the direction he could change it to and the angle of the rod while using it.
Some use about 1/8 inch rope for rod leashes. The easiest I have seen is to get a piece and put a loop on one end and a brass clip on the other. They used the loop around the rod and attached the clip to one of their D-Rings. For the right length, you'll have to experiment a bit and get it not too short and way too long. Good Luck,
Perry