If you are looking for a holder that you can use without drilling holes in your boat look at SeaSucker products. They are sold online. Not cheep but they are well made. I've been using them for a while and have no problems with them.
One set I use for rod holders and scuba tank holders. One olds my Garmin Chart Plotter, another has a drink holder, handhold, two holds my 2.5 HP Suzuki dinghy motor with some scrap starboard and I just ordered fore more today for a couple new projects. No ....I do not work for them. They are made in the USA and ship quickly.
I will drill holes if I must such as for my cantilever cockpit cover. I use the C-Otter for exploration, SCUBA diving and fishing. By using SeaSuckers the boat can be reconfigured for the trip easily. I do have a photo of the rod holders in my C-Otters mods albums.
Tom