I keep my spare engines on a shelf in the basement, in bags to keep the dust off, but not sealed so as to trap moisture. They rest on a cheap $5 rubber boot tray in case one decides to seep any oil, and I spin them over now and then to redistribute oil. Storing the engine in your house should be fine. For what its worth, I read somewhere that conventional 2-cycle oil does a better job than synthetic oil at sticking to surfaces over long periods of sitting. I don't have any first hand experience to prove/disprove that, however. I do use cheap 2-cycle oil to coat the insides of my extra steel tanks on the shelf, seems to keep them from rusting.
1985 Tri-Z 250
1985 ATC250R