My question is, is it a normal practice to have the liferaft out on one of the pax seats when flying overwater?
If you are flying alone, the raft needs to be where you can get at it when you ditch. Plus it needs to be secured, so strapped in the pax seat is a good place.
Twins crash just as much as singles, so yes a sensible precaution to take a raft in a twin.