I had a loose footed main and made my stack pack from my sail cover by stitching the lower edges together and unstitching the top join.
A bit of cutting and trimming then webbing strap sewn onto it where the lazy jacks attach except the lazys are not attached to the bag.
They are tied to the slugs in the boom. There is a stopper knot at the eyelets on the top of the bag adjusted so that the bag never carries the weight of the boom and sail even when the topper is let off. The bag will last longer that way.
There is a pvc tube each side but no zips or velcro. Just a simple flap sewn to one side wide enough to tuck down between the sail and other side of the bag to keep the sun off it. Cost me a couple of hundred all up.
Was going to make clip covers for the front and rear of the bag to keep bats and birds from nesting in the sail but the yacht got sold.