Go to Cboats.net and do a search, tons of info. I use Vynabond for Royalex boats to put down D-rings. The process of doing it right must be followed to the T or you can ruin your hull.
Don't use action packers, if you are running rapids or have beginners. You need dry bags or something that provides complete dryness, if there is any chance you can flip.
Once we were running the Moab Daily many years back, camped at Onion Creek and a group of boy scouts came down. They hit the first rapid, Onion Creek, and at least 10 boats flipped. They had no dry bags, nothing tied down, no floatation, it was a real mess. Alway rig to flip and use floatation, regardless of the water.
Not sure what part of the San Juan you are doing or when you are doing it, but there are a few rapids that can swamp an unprepared canoeist. At high water, it can be swift, and there can be sand waves. I would not recommend a metal canoe or a Coleman canoe with a keel.