Of course patience is necessary
But how many times will a marth approach from directly above? Your usmash should beat out his Dair, anyway.
Mansion is better then Cruise against Snake, I've found. On cruise, Snake's good at getting incredibly early kills off the close sides and his recovery is actually helped by the stage for any Snake who knows it (there really isn't anywhere that a Snake can't get back from with his cypher alone unless you're at the pendulum and it's swinging away from him, but one C4 and he's fine there, too).
Whereas on Mansion, yeah, being Usmashed into the ceiling is a problem, but Snake has much bigger problems to worry about (that being he has to approach you there, since nothing he has can go through the pillars). And Snake sucks absolute balls at approaching, putting the matchup heavily in your favor.
And I realize Cruise wasn't mentioned in your previous post, but I usually see people mention Cruise as a Snake CP when there are better options.
Btw, against Snake, ban Brinstar
That's one of his best stages...