Although now lapsed I was VSIB acredited, also used to be foreman at Hunter International with responsibility for all GAS/Electrical/water/Heating installs in trucks, these were large 4 axle trucks converted into horsebox/sleepers.
There is NOTHING hard, so long as you can solder, and have a very basic understanding of electrics.
It's like anything else hard until you know how, sure there are people who will get it wrong, and the need to keep it all mysterious so as to justify why only pros should do it.
Bit like the temp gauges on ebay for £40 the ones with a nice blue scale in F or C, look well smart, I buy these for £3, and one mod, sorry RESISTOR later, they work on 12v, as I can only assume people think it hard to modify to do 12.
Jesus, for £40 I would offer a 2 sensor version, and maybe even selectable different colours, again VERY easy, and cheap, about another £5!!