I agree with the rest of your post, but not the highlighted bit.
They were not lucky, they were well prepared, and if some dunce in a narrow boat with adequate power (i.e. not Ripple) tries to cross the channel in all probability they will succeed, it's just the odds of failure are rather higher than I like given in the worst case scenario it's an eleven mile swim to shore.
TD, for dramatic effect, exaggerates the danger, at one point Mon complains she'd heard the boat could have been snapped in half like a cigar tube. Given that all-steel narrow boats hang up on cills and the worst that happens is a bent rudder skeg this simply isn't true.
I liked it, but I found ND to Indian River more difficult, even though, curiously, I've cruised the intra coastal but not the canals of france. We also met them, and found them likeable.
That said, if we go it's either a trailable or a Dutch barge bought over there
edited to emphasis all-steel, narrow boats that are all steel not every steel narrow boat