I do not recall having to move the brakelines, even when I swapped from the original 8 3/8 axle, to a junkyard 9.25, and then had that Axle professionally re-bearinged.

My firestone ride rites have been insstalled since October 2007, they saw several hundred miles of Baja Washboard shortly afterwards, but that was also my last trip to Baja.

More recently they saw the Titus Canyon trail in Death Valley. There is about 10 miles of heavy washboard in the beginning of that one way route.

Mine do not noticeably lose pressure, not even after 13 years.

I have ZERO regrets with these airbags.

But New leafs springs designed for the intended load, within the GVWR of the vehicle, are ideal.
Airbags are not.

Rear passengers might think them too firm and bouncy. Rarely a factor for me, and screw those that complain anyway.

Your Van sagging with new rear leafs, perhaps indicates you have too much weight, and if so, that makes the brake performance a top safety consideration.