I always run 2 per deck, you could run 1-2 Ruins of Alph and 1 Lost World, this format only has 4 legal Stadiums, 1 exclusive for legends that nobody uses and the unreliable Burned Tower, only Marowak can discard stadiums, so don`t worry about losing RoA, just play carefully, since you can get an autoloss if you play LW in the wrong moment.