I installed a climate control system inside a storage box at a local university many years ago. It has worked very well over time for this Steinway D.
First I lined the box with 5 mil plastic using a staple gun to seal it, top, inside doors and sides. I was thinking giant moisture shield. I placed four dehumidifiers low on the side walls and a double bucket humidifier about two feet off the floor on the most easily accessible side wall. I built a wooden barrier to protect the humidifiers and provide an inside connection to mount the buckets and mounting rods have moisture shields in place but not too close about 6 to 8 inches above the buckets. I cut a hole in the side wall for the warning light panel and the fill tube to exit. AC outlet is inside the box. We put the box along a wall of the building and ran electric into it for power supply. I also built a padded "chair rail" inside to protect everything when moving the piano in and out of the box. Depending on the ambient humidity on the stage we move the piano out of the box (sometimes it stays in the wings) up to 72 hours but usually 48 hours in advance of preparation for the concert. If the room is around 70/40 things go very smoothly which is a lot of the time in Spring and Fall.
We have 4 full seasons here and the piano has stored through the seasons without significant pitch drift. I sometimes let the pitch float in the summer but never above 442. The rest of the year it's always at 440. The stage manager has charge of filling and supervising the moving and after all these years (knock on wood) no tragedy has occurred. We use a piano transporter for the moving and it stays in the box under the piano ready to go. We remove it on stage. So no wires, no beautiful piano trucks. The stage manager and I worked to train the crew to remove and replace the transporter correctly and it was worth it. The cabinet is remarkably unscathed after 20 years. The only real damage came as the result of a stage light falling from the mounting bar above the piano. Fortunately damage was confined to the front piece of the lid and repair was done without much gnashing of teeth. We all learned a valuable lesson about leaving the padded cover on as much as possible. I'm not sure what the lighting technician learned but so far no more lights have fallen at this venue.
Chris Solliday RPT