My 71 has (or, I should say, had) factory A/C. The windshield washer bottle is up at the rear of the trunk in these cars, and secured in place by a rubber strap. The strap hooks to a nice, sturdy bracket where the bottle sits, on one end. On the other end, it hooks over the cardboard divider, which covers the blower fan, etc. Over the years, the hook has really done a number on this part of the divider - it is broken and bent in that spot, now.

Has anyone worked out a clever way to hold the bottle steady, without using the cardboard divider as an anchor point for the rubber strap?

It isn't easy to relocate the bottle to its normal spot, under the front latch panel, because the A/C condenser fan housing gets in the way, and I would have to weld in a support bracket for the washer bottle, too.