On mine there is a flange on the rear of the tubes that goes around the cutout in the transom, It is held on with curved aluminium plates that sandwich the flange to the transom. The front strips along the side are not straight, they have a definite curve upwards as they near the front from about halfway along.
I will be refitting my tubes shortly, not a job I am relishing to be honest. There is something like 360 screws that hold them on.
__________________
|