Have you already purchased them? Do you know what type you want? Permanent or take off?
I prefer the removable ones (Scotty or others) for ease of install, you can put on numerous bases and move them around, easy to add an additional base later on and you can fine tune the angles and direction of each of them. Also, you don't have to cut big holes in the boat. If you need to move one, a couple screw holes are a fairly easy repair.
A lot of downriggers have pole holder attachments on them making for a nice clean install.
I have 10 bases and 5 holders on a 22 in addition to the 2 on my Cannons. As far as do's and don'ts: "Cut or screw into your hydraulic lines or electric comes to mind". (It's a don't) :lol: All those holders and we may never have another salmon season around here.
Chris