Passing cables through a thermally insulated wall
Having done aerospace environmental testing, I'll give you the method we used. The ovens had several ports in the side bigger than any likely cable. For a given piece of equipment the necessary cables were passed through the hole, than a piece of foam was used to plug the remaining apertures.

Don't worry overmuch about the heat/cold loss through a few inches of foam. If this does indeed make a critical difference, your heating/cooling system is underpowered.