Is there a possible way Rotom heats HP,Def,and SpDef stats goes more than 300 with a bold nature?
I want its HP,Def,SpDef to go over at least 300 at the same time.(No cheat)
Sadly, that's impossible.
But with this EV spread: EVs: 252 HP / 96 Def / 160 SDef
He will get 304/301/290 bulk spread with Bold nature.
That's about the best you can get.