Actually, in the rules it doesnt even say you have to write to wich coast you support. That means Gas S MAO-SPA is valid. At least when playing FTF the normal interpretation is that IF you specify coast it has to be right. So if I write Gas S MAO-SPA/sc and the move is ordered to Spa/nc then it's an...

the coasts are not separate territories. so the thumb rule "you can support to a territory you can move to" still holds true.