Some comments..
The GG Mariposa (Plus) does indeed take "clothing" as padding for the shoulder straps. A mate of mine has one...
However it should be remembered that it is a 23 oz pack meant to carry a max weight of 30 lbs and really only comfortable (for me) at under 15.
By comfortable I mean that my shoulder won't ache after a few miles.
Compressed clothing offers very little if any "cushioning"
Or to put it another way , I would not even use that as a day pack...
As far as
"All the pockets for the "padding" will have liners made from ironing plastic shopping bags together making them water proof"
they will not stay waterproof for long .
Franco