First off, loto is rotating. Which to me, means you need a more reliable damager than rainbow. Spiritomb TEU and jynx from unified minds could work, or you may not even need spiritomb since your opponent will most likely help you out by damaging your stuff, or you can play shrine to tick damage onto shuckle or dedenne. The jynx lets you move a damage counter anywhere on your board (but only on your side unlike banette gx).
This means you can play all grass energy and use viridian or spinner if you want to search it out. Rainbow until rotation is probably fine, although po town is possibly better (you can recycle it with a lusamine instead of needing to use oranguru and possibly falling behind a turn in the prize race. Plus you have no stadium, so for instance black market ruins your day right now. Po town would fix that as well).
Post rotation stadium could be anything, but viridian is probably most useful.
Second, Guzma will also rotate, so you either need a different gusting card, or maybe you don't (they're going to try to KO you with their one prizers if they have them, though, so ideally some gusting option would be good even if just custom catcher).
Third, since you have to take 6 prizes, this deck is always going to have a tough time vs. one prize matchups, unless you can tank their hits somehow. Shedinja only keeps you in the prize race if your tanking pokemon can stay alive sometimes.
Shuckle will work against several non-gx decks, but welder decks and some malamar builds will slap it hard for 2 prizes, and others will drop a power plant and go.
Suiciune GX might be an option, if they can't ohko it, you can switch into beedrill and shuffle the damaged one back from the bench.
Another interesting option could be rowlet and alolan exeggutor, since it can set up your first beedrill (or more ideally, a meganium that then chains your beedrills), and with a weakguard energy attached, it would be able to tank most hits plus you could play gardenia to heal it.
You could even try donphan and last chance potions, but spread would make you sad unless you also played something like a shaymin.
Baby melmetal and metal core barriers could be somewhat effective as well.
You'd really want to play around with it and see if any of these ideas are worth anything.