For the seeds you can cover them to keep the RH up until they are sprouted but take the cover off once up so they don't end up with stem rot, (damping off).
The best way to raise the RH in the grow room is get a humidifier. One that uses evaporation or a fine mist is cheaper to operate and won't add heat to the room. I generally find one at the local thrift store but haven't seen any this fall.