Are you confident of being able to sleep through the combined
noise of the A/C and genset on a 39 footer ? You might find that the
noise is hard to escape.
The claimed
fuel consumption of that unit is rather high at .88 gph. That size of genset should give 3 or 4 gph.
Just for the
record, I have A/C on a 43 footer and hate it. The unit came with the
boat.