Niko as long as you use shielded cable to the dew heater it will be ok.
If you want to be sure of no RF interference then you make a voltage controller without PWM but it will need a larger cooling block.
If you are on AC power it doesn't matter much but when you use batteries it is a waste of power.
I run my heaters on 12V all the time and that works ok with the refractor type of scopes.
With reflectors it will be different
If you make it yourself with LM voltage converters then you can make all the channels you want and expand later.