I've got a very expensive storm proof tailor made cover, can't remember the manufacturer offhand, but will dig out receipt later.
I would advise against using the indoor cover underneath , as it will prevent the outdoor cover from breathing and both covers will go mouldy.
Got mine from classic additions. Got the ultimate cover and it's been really good. Make sure it's strapped down well and it won't then move around even in high winds. I had no choice other than store outside too. Plenty on here will say don't bother and just regularly wash, but sometimes mines sat up for a couple of weeks, so it gets washed before the rover goes on and then it's clean still 2 weeks later rather than having to keep washing. Always wash before the cover goes on though otherwise dirt can be rubbed by the soft inner fabric causing tiny scratches.
Was told by classic additions 'don't' put indoor cover underneath though, as like others have said, you'll get damp build up between the covers and subsequent mould.
I can vouch for not putting a cover underneath your outdoor cover...everything gets soaking wet as there's no 'breathing' going on. I bought an expensive outdoor cover but try as I might, I couldn't stop it from marring my paint in certain areas. This year it's in a Carcoon.