If the air conditioner (not heat pump) is the same as on the smaller Bambi's, the "optional electric heat strip" is easily installed. It just plugs into a socket and gets bolted down. Since the strip is accessed from inside your Airstream, its presence does not affect the overall height of the A/C shroud.
The heater was optional on our 19' Bambi, so I bought the strip from an RV parts store for about $25-30. Then, when I removed the interior A/C cover to install it, there was a heat strip already in there; so I took the new one back and got a refund.
The heat strip is actually round and looks kind of like an electric stove removable "burner", except there is only one tubular loop, instead of the stove burner's flattened spiral. However, before you purchase a heat strip, you should probably check to see if one has already been installed by the factory.