Interestingly enough, I was having the same problem. I think I'm going to playtest Despair Ray Mega Gardevoir/Max Potion/Darkrai GX. It sounds absurd, but hear me out.
First and foremost, it's resistant to Zoroark, OHKO's Marshadow without discarding and part of your bench, and Max Potion paired with 4 Mega Turbo keeps the same Gardy alive for more turns, which is like using another Gardy to Despair Ray away, but without actually getting rid of it, so you get more time to set up. Darkrai GX is literally just there to put itself on the bench to discard. So, why play Darkrai at all instead of Exeggcute, when putting itself back in your hand is better because It's Ultra Ball fodder? I actually forgot why... Only situation I can really think of right now is if somebody Pokepuffed or Target Whistled it out, which would work anyway since the deck would still be playing 1-2 Egg copies. The it problem I would find is trying to get a giant OHKO on a big GX, which I guess isn't even what this deck tries to do.
Your initial plan of playing Turbo Turtles is also a good choice, since Turt can OHKO Zoroark, baby Volcs OHKO night marchers, and Turt can OHKO a marcher with Shell Trap, forcing the opponent to attack with Marshadow, Zoroark, forcing to play a Guzma, or accepting the prize trade, none golf which Night March likes to do.