The 3d gloop mentioned in the video is a solvent that’s used for welding PLA. You could definitely use that to properly seal it. And being built from blocks like in the video (which is due to a limitation of the size of a 3d printer) means that any leak would probably be limited to a single block at a time and probably not catastrophic.
Fiberglass may be overkill, but you would absolutely need some kind of sealing lacquer around the entire print or it will definitely fill with water.
Honestly, some two part epoxy smoothed around it and you’d be gtg. And getting high off the fumes it gives off for the next three years…
Alternatively, build a siphoning drain tube so your movement over the surface sucks the water out as you go.
Then you just have to not stop paddling.
The 3d gloop mentioned in the video is a solvent that’s used for welding PLA. You could definitely use that to properly seal it. And being built from blocks like in the video (which is due to a limitation of the size of a 3d printer) means that any leak would probably be limited to a single block at a time and probably not catastrophic.