I have always used car paint rattle cans to paint Tri-ang and all my other model ships, including plastic ones, and never had paint-peeling issues like you.

Which begs the question - what sort of paint are you using?

I have occasionally used a primer on the bare metal, but normally spray the colour straight on. I think it always helps to use the 'hair drier' technique with rattle cans.

Warm the casting first by wafting a hair drier over it. When you have finished spraying (one side for example) waft the drier over that to help the paint dry quickly. It also blows any residual paint away from yourself. BUT! DO NOT USE THE DRIER AT THE SAME TIME YOU ARE ACTUALLY SPRAYING.

Spraying works best in a warm and dry atmosphere. Do not spray in a humid or cold space. I always use my garage when conditions are right.