What is best to coat the kaowool in a gas forge, but is it really needed?

ITC100. Makes a huge difference, imo.

is it really needed?

for one part it depends on how its used
the forges at work can have 4 smiths trying to stuff all sorts of shapes into and out of them at a given time,
to say its hard on the lining is an understatement

Kaowool is a good insulative, but even coated a very poor structural surface
adding something structural makes it the oxidizing surface, but it will have far more thermal mass
meaning it will take more time to heat, slowing the forge from getting up to temperature.

Ceramic furniture or tilerefractoryfirebrick linings provide far better protection from the odd piece of stock
slipping off the support stand and gouging the ceilingsidefloor


on the other hand a refractory lining will retain the heat for longer than a lighter insulative,
meaning it wont take as long to get back up to heat if you take short breaks