According to RBM rbm2(remove :
Damn Chris, it must be that Canadian air, I can't get a liner to last more
than about five years, and even at that, they start to shrink and pull away
from the bead. I wouldn't even worry about the bottom, just hope it stays on
the walls

The SO corrected me. It's actually 19 years old - installed 1987 ;-)

The water will push the vinyl back against the walls alright, I'm just
a bit worried that if the vinyl along the bottom edges doesn't slide
back into position, either the vinyl will tear or pull out of the
rim ("bead" I guess). Hence my question about trying to "help"
the water pressure stretch out the wrinkles. But how?
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.