What you'll need to do is find the water line on the boat... where it sits when fishing. Make sure its level across the boat... level is very important on SI imaging. You'll need to mount the transducer below the water line but above the water when on plane. Also make sure the motor or other obstructions left and right of the transducer are not blocking it... you need a straight path from the side of the transducer to the bank in other words. If the motor blocks the path when it's trimmed down, you can always trim it up a little when you're scanning. If not, you'll have a broken image a jet trail on your screen where it's blocked. The transducer does not need to be in the water on plane... the drag of running higher speeds and the chance of knocking them off isn't good on them and they are expensive to replace. Buy a sitter and a separate 2D transducer to epoxy inside the hull for traditional sonar.
Some things to consider... the left or right path can be blocked and it still work. You'll just lose the portion of the scanning area which is obstructed. Some guys do mount the transducer low enough to be in the water on plane. I don't and don't advise it due to cost of replacing them. Knock a few off and you'll see why. With as much trash as we get in the spring here it's easy for a limb to pop up and hit them at lower speeds. I've broken a small 2D transducer that way. They make a transducer saver to help with limbs and would recommend one in your case. Try use epoxy to secure some kind of mount... I've seen people use a hard plastic kitchen cutting board square, to the boat instead of drilling holes in the boat to mount the transducer. It'll get it off the transom a little further and if it doesn't work in the location you don't have holes to fix when you move it. I'm sure you can Google "SI transducer locations" and see pics and get some ideas. Like above, level with the water line is very important. Left to right level and also front to back level... sit the boat out and adjust the jack position up and down until the water line of the side of the boat is level and then check the back... I'm sure you know but using a 4 foot level or longer is best.