I had one of those free standing ones Lowes sells. that darn thing put out more heat from the discharge hose and housing than it put out cold....bad deal I guess. you also need a drain hose too. I also had a small cab then too.
Then I bought an APU, thought it was good to go, the install was bad, the price was high, and the customer service was horrible.
Reference in this forum HP 2000 APU.
I rebuilt the unit myself. it is a good unit, just the wrong people sells it. Light, and is not generator based, it only has an alternator and a auto A/C compressor and has a heat pump switch for heating. It does pretty good after working out all the bugs....none of these things are perfect and are priced high.
I did have a generator and a window unit, I would rather rent a room instead. I do see guys with the unit cut out a hole in the sleeper....I don't know
I have seen a compact unit that bolts to the back of the cab with a generator, then you have to have gas...I got up at night and had to fill it with gas....crap
If I do another one, it will be the all electric/battery based, and then maybe a small generator for emergency backup.
Idle Smart has a module that hooks into the ECM and starts your truck to keep the batteries charged... 913-744-4354 or firstname.lastname@example.org....it is pricy too, but next to the HP 2000 or any other APU diesel engine based, it is around half the price.
Happy Trails, cool nights