The lines and the inside , but the lines and inside unit must be evacuated.
A vacuum pump can be purchased reasonably from Harbor freight, but you need to be sure that there are no
leaks by having a gauge to read very low necessary numbers and verify leak free.
I used a Harbor freight vac pump and my company had gauges. I have installed two of these units (Comfortaire) the first on the 16'
Scamp and the second for a Florida room at my "new" house.
I have found them to work well. The installation is complicated if you have a poor quality lineset with poorly formed flare fitttings like my second system. I had to remake both ends and I might as well have just bought copper lines rather than line sets.
By the way the COmfortaire I used is an inverter unit and runs well from my Harbor Freight 2500 watt inverter
generator and would probably work just fine with any of the inverter 2000 watt units as well. There is no starting surge and perhaps 9 amps at full load.
It seems to be very efficient and quiet and provides heat down to a pretty low temp. For backup I have a small ceramic heater