[PeterM]

Outside only. I've had 4 SCTs over the last 6 years and never had need to clean inside one, and usage is typically 100 plus nights per year averaging 5 plus hours per night so a lot of use. Mind you they are housed in an observatory and aside from recently using dessicant blocks in an eyepiece plug I never cover the front of the corrector with its metal cover. Instead I drape an material type Aussie flag (any will do, bought from the $2 shops) over the corrector (not touching it) this keeps dust off and allows everything to breathe, remember its in an observatory but the idea is the same if can be left safely that way, also bets way for Newtonians let them dry out don't lock it in with end caps.
We have had a Meade and a Celestron SCT in the shop with very obvious and significant mould on the inside of the corrector and have rectified these and not seen any obvious resulting damage. These were really extreme and I would talk with whoever you bought from before undertaking to remove a corrector.
Don't panic, oh and don't spray, tip etc any cleaning liquids onto the corrector when cleaning, it's too easy for it to run and will find its way down the sides of the corrector and almost certainly onto the black paint inside tube leaving white streaks in the paint ( I did it years ago). You will need Dons cleaner (Bintel) & Blower brush, Lens tissue, Microfibre polishing cloth, Orion have these in packs (we stock them at Sirius) and there are lots of articles on how to clean successfully on this site and by Googling.