First I addressed mounting of the heater unit. I decided to put it outboard on the rib because the inboard has a bump and I didn't want to deal with spacers or extra stuff. I thought about how to remove it later in life when the wing is sealed up and you have to work only thru the access hole. I decide nuts with bolts would be a pain and decided to mount platenuts on the heater unit. This way I'll just push in screws and tighten them up. No messing around with nuts and washers on the back side of the rib.
I removed primer where the unit mounts so it is grounded and I'll use one of the mounting screws to ground the ground wire.