Right I'm sure I can describe this without pictures, might just takle a thousand words.
First thing is I don't ferment in a bucket. I ferment in a plastic beer brew barrel, pretty solid, holds 5 gallons and is the same as the one I rack into to store and keep the cider.
The barrels are pressure barrels and have a tight sealing lid with cork in the middle through which the bubbler goes and yes I drill a hole for the power lead for the heater. The heater hangs submerged in the liguid hanging from the cable, it does not touch the sides. A bit of sealant round the cable seals it
I have three barrels and two heaters, I brew 2 barrels at a time, one just before the other so I can rack the first ferment into the clean barrel, then the second ferment into the first barrel, leaving one barrel left to clean. I can do multiple racking this way. I have different barrel caps for racked cider so I can top up with CO2 as I drink.
The heaters are 100W and 200W, 100w seems plenty and spends most of its time off. They both have adjustable thermostats. One is glass and one stainless steel, which seemes Ok but I think glass would be better for cider because of the acid. You can buy beer heaters but they are just the same as aquarium ones except more expensive. 'Beer belts' heat the outside of the barrel which seems wasteful andless effective to me.
One last thing I wrap a towel round the barrels to keep the heat in.