weather proofing a swag

Set it up and put a sprinkler on it for a while or wait for a rainy day if you have restrictions [raining here in the Isa] and let it dry , Or you could get that special spray in a can , like the stuff for car upholstery , if you spill coffee or Coke it sits on top instead of soaking in

Disco123
You need to soak the swag with a minimum of 6 hours solid rain (or in your bathtub ),
Then dry out in the sun this is important to make the cotton thread swell in the holes it made in the canvas when stitched. It is not actually doing anything to the body of the canvas this should already be waterproof, Some canvas products can take two or three soakings to completly stop seaping at the seams.
Good Luck
Derraux

Just fill your bathtub and keep it submerged for a day then set it up and let it dry out and do it again if you can....
Take out the mattress...

yep, submerge it for a few hours, then dry it, then really soak the stitching again.

don't use a waterproofing agent on anything other than the stitching, and even then only after a few good goes at wetting it down