We've already started some general fitness training as well as some core ski exercising, but are there any tips/tricks that those who regularly get this sort of skiing in might advise?
Saint, your profile says South of England. Do you go to the indoor ski places some? You could do some frequent regular sessions at those places for 3-6 months before your trip, that would help build/maintain a nice fitness base. Hemel or Basingstoke maybe? The slopes aren't particularly challenging, but up & down on the Poma for hours definitely builds the base.
As a bit of a funny side story, some years back I had frequent business trips to the UK from the States, and I used to bring my skis along on the biz trips and then every evening after work drive over to the Snow Centre in Hemel Hempstead and ski til closing. It was super fun! And helped maintain ski fitness during the US off-season. I didn't tell anybody at work though hahaha