Best Waterproof White Paint for Bathroom Radiator Refresh: Roller Application & Primer Advice

I warmly welcome,
I need to refresh the ladder bathroom radiator, because the paint is peeling off it, so that there is rust on the top. The previous owner of the apartment fixed it in a very unfortunate place: centrally where you take a shower, i.e. every time you take a shower, water flows onto the radiator.
I wanted to paint it with good white paint. I wanted to do it with spray paint, but I would rather not spray it on the back of the radiator (between the radiator and the wall)
I also need white paint for canned radiators (so that it can be painted with a roller), which is also very waterproof. What paint do you recommend?
To do it properly, do you need to give a primer or not?
Thanks in advance

It is not that simple. This radiator is painted rather with stoving varnish (oven-baked). You would have to start by thoroughly cleaning at least those elements from which the paint has come off. Later, you need to give a primer (maybe red?), And only a topcoat. I would rather take a measurement, and this radiator, I suspect, is typical, it is mainly about the width - to be connected, because with height you can always be a few cm shorter. And the cost? I think 200-400 zlotys don't worry. I do not see any problems with replacing the radiator - 2 valves, so there is no need to empty the water from the entire system.

What was on this radiator is powder paint, nothing better was invented for the radiators. It can be regenerated and will be like new for many years but? is it worth it. Old paint has to be carefully removed and cleaned to living metal, it is already so laborious that? Then you go with him to the company of the powder coating plant, they apply the powder and heat it at 150 C, it is like new. Painting cost ~ 80 PLN and a lot of own work.

I did it once, but only because I had no hell to choose a radiator as it was and I felt more confident in painting the radiator as in forging and remaking the installation under the tiles. First of all, I used a paint exfoliator, after scraping with a spatula, the grinding brush was started on a drill very annoying, time-consuming and irritating, especially at the ends of the tubes. Then the primer and renolak went where I could, with a roller, where not the brush, also very annoying. Lots of work and how could I just buy one, I would not even think about it.
In fact, if I had such tiles or were able to get it today, I would forge it and remake it and set up a standard available today.
Effect? Well, the drama was not broken. In fact, I wished I had tried the pistol.