Any electrical insulator will work. I am not a fan of Great stuff foam because it makes a horrendous mess, and will offgas some nasty gases over time, that then will likely condense on things like the clear plastic on radio dials.

And old cardboard box can be cut up pretty easily to make the insulation layer, and you don't permanently destroy the trash can if you need it for something else later.

I suppose an old towel or blanket would work as well.

The other thing to be aware of, is the trash can joint and any pinholes needs to be covered with that foil HVAC tape. The slightest path for the EM to get through, really spoils the protective effect. There is a guy on Youtube that demostrates the amount of DB shielding by using some fancy equipment he has in a lab.