isolating the room with exhaust going 'elsewhere', any which way and not intermingling again. anythign that achieves that can help, but the simple fact is if your dehum cannot keep up with your plant's moisture production and your natural ambient climate of that room, then you need a larger dehumidifier.
if you are set up properly already, then you need a bigger dehum. Try optimizing by exhuasting to a different area or outside and make sure that room is relatively sealed up as far as ambient RH% penetrating/adding to the room. if the dehum cannot keep up in this context, you either need a bigger dehum or only grow in seasons with less ambient RH%. I switched to winter-only growing for this reason. I need a humidifier the first 4 weeks but after that i need a dehum controlling RH in what would normally by a very arid environment. Makes good use of some of that heat for the rest of the house, too. Scale up and grow in best season. Lots of economies of scale to gain.