Absolutely fantastic read. The author got nerd-sniped HARD by these missing-person cases and his approach and accomplishments are inspiring, to say the least. Very well done!
For the ROV I was wondering why not build something heavier than water but have it on lines attached to buoys, then to go up/down you just climb or down the ropes. Not as maneuverable but not certain if it’s significantly less maneuverable.
"It's always in the last place I looked"
I think we're seeing the first few guesses for where the car might be, but according to the author, there was a 40km distance between the cabin and the girlfriend's town.
Hindsight is 20/20, but I wouldn't put it past the author to commit beyond 3 search sites, some of which may require deeper and larger bodies of water (like the second investigation did).