The 110 and LP connections were made before the unit was slid in from the outside. The 110 line comes into the box via a 3/4" hole in the box. It was then screwed to the flange on the outside with about 20 screws.
Sorry to disappoint all the haters of this post but I am smart enough to see that a totally enclosed plastic cargo bay does not allow access without either cutting a hole or removing the whole unit. The element and relay are in the rear of the heater.
I cut about a 12"x12" hole to access it. The relay was bad. Not the connections or element.