I have a problem with the use of the function key, follow me.
I have to build a “rubber” all around the tubular rubber boat as in version 1 of the drawing, but in version 2 is not possible.
Here’s what worked for me. I made a copy of the hidden linear elements of the pontoon that constitute a Follow Me path and positioned a copy of the rib profile on it. The extrusion worked fine outside the environs of the boat group, so I then just positioned the rib extrusion and its flipped copy on the pontoon, intersected them and cleaned up the overlap at the intersection.
Okay, so I made a single group out of the new rib geometry, and it proved to be a solid. Then I scaled it from side-to-side by .995 to be sure it would intersect with the pontoon all around. Then I performed an OuterShell between the boat solid and the rib solid. To my delight, it resulted in the required single solid.