I use a yoga mat (thinner than a sleeping mat).
A layer of tape over the holes. A layer of foam that completely fills the rim. A split tube on top of that.
It seals well enough that it goes up with a hand pump without sealant.
Added bonus is that it actually seats the tyre on the rim properly, with a tube it tends to get stuck in the bottom in places which is why it peels off in others.
There’s a lot of on-one bashing, but thats mostly because so many people have them, and therefore have problems. The rims are the same extrusions as plenty of more expensive rims, and the tyres are as tight as any other brand.