i use a rod holder very similar to that one that you have pictured in the first picture. basically just an adjustable tube from scotty. i got around the mounting issue with those mounts by bolting the mount to a small board 9"x2.5"x3/4". (i used a piece of the green pressure treated lumber that resists water damage as well) this way the mount has stability. i then got industrial velcro (2" wide) and made 2 straps for the board. i mounted them toward the ends of the board so they would hold the board solidly. then i velcro the board to the crossbars in the canoe. my group rents canoes because we are younger and cant afford our own canoes yet.

this velcro setup really is nice because it holds super strong. i can lift the whole canoe by only grabbing my rod holder, not that i would suggest doing that though. my father has a small woodworking shop so i used a router to round off the corners of the board and countersunk all the bolts. i then used contact cement to mount non-slip rubber to the bottom of the board to create a noise reducing and solid grip for the rod holder. then i spray painted the whole thing so it looks professional. the velcro makes it super easy to move around and even change canoes if a buddy wanted to troll and i didnt want to.

by using a adjustable plastic rod holder like the ones from scotty you have a lot of options as to the angle of your rod. to avoid the loss of line tension when you take the rod out of the holder, i always angle the rod forward  and make sure it is out the side of the canoe that i am paddling on. this way i can lean forward and pull the rod out and keep the tension and (i use a baitcaster) spin the star-hub drag tighter. then i pump the rod a couple times to ensure the hooks are set solid and go from there.

also the adjustable plastic rod holders just twist and lift to come out of the mounts. i leave the board strapped to the canoe on portages and just toss the rod holder in my pack so it doesnt hang in the way.