Insulating a 300-Liter Galvanized Boiler: Applying Mineral Wool for Enhanced Heat Retention

My 300-liter hot water boiler cools down quite quickly and the reason is obvious - no thermal insulation. The boiler is heated with electricity in the second tariff 26gr / KW / h with a 4.5KW heater. In winter, it didn't bother me because possible heat loss from the boiler warmed the bathroom, but warmer days are approaching so you would have to think about some thermal insulation.
I have an unnecessary pack of thick mineral wool so you could use it.
My question, how could the galvanized boiler be lubricated so that when applying wool it sticks to the metal sheet a little?

I will tell you that the glue for mineral wool in spray, i.e. in foam

And you intend to inhale dust from this wool in the bathroom every time?
As soon as you wrap this with wool, fix it with a good tape and then wrap it tightly with some foil, stretch and preferably the foil with a cover for zippers and it will look civilized.

I didn't write one. This insulation does not have to be aesthetic because the boiler hangs horizontally on the ceiling in the bathroom, and below is the second suspended ceiling and the boiler can not be seen at all. The point is that the insulation should stick to the boiler.

It's wool and narrow stretch from sandwiches and riding ...

It would be good to wrap the wool on top with aluminum foil and then stretch.