I have a 3kw mains immersion element in each of my van tanks.
As posted above, the main benefits are supple non-kink hoses and non freezing of jets. I tend to heat to about 28 degrees in the (insulated) tank and other benefits are that the pumps and back of van are kept well above freezing as my tank has a gap in the insulation to allow warmth to spread out.
By the end of the day the temp. has only dropped to about 20 degrees and so still usuable.
Round here this week the days have started at about -3 and crept to about 0.
If I hadn't had heat I think I would have still worked but started much later and finished earlier.
We take a broom and grit/salt to ensure no freezing.