I agree. I'm already stuck with a rooftop A/C but if I had a choice I'd
opt for a central heat pump/furnace mounted under the oven or under the
floor. Easier installation and removal (they all die someday) than having
to have a hoist set up to deal with its 120#+ on the roof.
As far as doing w/o A/C, our trailer gets like an oven on a hot day, just
like any vehicle and like any house with a 6'-2" ceiling height. The
reflective aluminum skin helps I'm sure but the only 2" insulation
doesn't do a whole lot. Parks with lots of trees are nice but are not
everywhere.
Most roof vents for many years have been 14" square. Our trailer has 4
roof vent holes with the A/C in the second from the front. If it had
those nifty $200+ each powered roof vents maybe we wouldn't need A/C but
since we have a heat pump it's good heat in cool weather.
As to wind drag from rooftop A/C, the A/C is in a sort of "dead" area
along with TV antenna, sewer vents, and roof vents. There is actually
quite a lot of lift on the roof at speed. The air stream does not follow
the roof closely. Awnings also look like a lot of drag but the same thing
applies. They are in a "dead" area on the side.
Most anything back a foot or two from the curved front edges and
"corners" that does not stick out more than a few inches doesn't have
much if any effect on aerodynamic drag.
Source for concepts: Automotive Aerodynamics (by Norbye?) book loaned out
to auto tech friend in OR.
The A/C adds at least 6" to the clearance height of my trailer - I'd hate
to scrape it off on a gas station awning or tree limb.
Al