Which willow cans? There seem to be two main types going the rounds.
There are 25L Blue ones, clearly marked hdpe or with a triangle with the number 2 in it, signifies food grade plastic. Lots of homebrewers use these and nobody seems to report any problems.
There are also 20L Blue ones, a little bit thinner and less "blocky" in appearance. These don't have the hdpe pr "2" mark. Some brewers use them happily and some avoid them like the plague.
I have the 20l cans, and I have had one truly bad brew using them. My cooling practices on this brew were horrifying, and I think it would be unfair to blame the Jerry. The rest of my brews conditioned in these cans, I have been happy with. I can also fit 3 of these in the conditioning fridge, and only 2 of the 25l ones.
Maybe this will prompt more informed posters to tell what to do.