Also, if it's at all rusty and you don't get it all, the rust will continue to develop.Tub paint has a high failure rate when it comes to diy. It's difficult to get it good and clean. Is it peeling everywhere or just certain spots? I don't know if they steel make cast iron tubs - it's probably steel.
The kits might look good a month or so, but you definitely didn't prep correctly. As an example you have to first get rid of the soap scum, lime, rust, and caulk. Then rub alcohol. Then scrub with like a "0" steel wool. Alcohol. Then like 300 grit. Alcohol. Some kits will provide an etching chemical.I sanded fairly well witht a sand block. Then wiped with a wet towel and waited for it to dry. Then brushed on the paint.
I can't imagine you got paint to stick to cultured marble or manuf/natural stone, so I don't know what else the counter would be besides laminate.It’s the alcove type. It cracks in some places but not all over. The bathroom countertop is not laminate, idk what its madenof but it’s solid not hollow.