It is possible for water to go down the exhaust tube through the exhaust port and into the motor. It is just as possible on a 4 stroke via an open valve. Any water in the exhaust would drain out straight away though.

On a 4 stroke the motor oil will leak out or possibly flow into the combustion chamber if it isnt stored more or less vertically.

Either way petrol is likely to leak out of the carbs.

Try making a stand out of some 100 x 50 ... maybe something nailed to a saw horse would do the trick. even a bit of 4 x 2 nailed across a couple of studs in the garage .. or better still rip of the gib board of the wall in the spare room where the wife never looks and nail something to that