Problems with vinyl upholstered cushion

I’m making a camping seat from a 5 gallon bucket. For those unfamiliar, you basically make a round vinyl-covered cushion and glue it onto the lid of a 5 gallon bucket to create a portable, padded seat.

The problem I’m having is that the ‘cushion foam’ I got is so cheap it totally collapses when I sit on it. To the point where I feel like the vinyl is going to pop from all the trapped air trying to escape. (And for some context, I’m only about 120 lbs, I feel like there’s a good chance it would if someone larger sits down) I think the only reason it hasn’t popped just from me sitting on it so far is that the air can somewhat escape out the bottom of the cushion (the way you make the cushion is you wrap the foam in the vinyl and then staple it down to a cardboard disk on the bottom of the foam) but once it’s glued down to the bucket lid I don’t think the air will be able to escape like that.

So I’m looking for solutions. I don’t know how readily I could get my hands on different foam, this was the only thing I could find available locally. I thought about maybe setting some eyelets in the vinyl to create ‘vents’ but that kinda defeats the purpose of making the seat out of vinyl since it’d no longer be waterproof.

If anyone has any thoughts I’d be grateful : )

Could you remone the cover to add something under the foam? It doesnt need to be pretty so you could sew a rough circle shape & stuff it with polyfil, chopped up fabric scraps, layers of quilt batting, bits of foam or some other soft thing that would add padding & prevent so much compression. The cheap squashy foam you currently have would make a smooth surface over that but evenly distributing whatever you use will keep it from being lumpy when you sit on it. To keep it from potentially popping, pull it pretty tightly over the cardboard disk before stapling. That way there will be very little air that needs escaping but still test it & if it really needs a hole, add just one or 2 eyelets.

I’ve done a little upholstery & even though this is a simple camping stool, you can get a pretty pro looking finish by evenly pleating the vinyl around the disk. That might increase even distribution & comfort too.

I have made cushions for tubs like that…but like @magpie said, I used a round wooden piece, put the two foam cushions on it, wrapped the cushions with batting and pulled and stapled it to the wood piece underneath. Then, I wrapped a lining of cheap white fabric and then the good fabric…by using the batting and the lining, it squished most of the air out to make a firmer cushion. I then put the whole thing on the tub…I did not glue it down at all so it could be used on any tub. I have to warn you, though, heavier people might not be able to sit on them as those tubs are not meant to hold much more than 200 pounds I think.

Maybe add some mall grommets to the sides or near the bottom of the vinyl to let the air out.

COuld you add a hole to the plastic lid under the cushion to let air out? Then it would still be waterproof as long as the lid is on the bucket. Assuming that the lidded bucket isn’t airtight, I guess.