And then there's always Plan R... for redneck.
Because I'm a weenie and would grimace at the thought of cranking up that extra 80 pounds or so every time we set up camp, especially at times and in places where air-conditioning was not an issue, I removed the A/C unit from the top of our Viking and replaced it with a 12-pound, 12 volt, 3-speed, in&out fan with Lexan skylight dome, Model 4000 by Fan-Tastic. It fit perfectly, by the way.
Since we live and camp a lot off the grid in Arizona, to meet the occasional A/C need we bought a 40-pound, 5000 btu, 2-speed household room A/C unit by LG about the size of a small microwave at WalMart for $80. It only draws a little over 500 watts, the perfect fit for our All-Power 1KW generator, which weighs in at under 40 pounds, and can still be found for about $130 at Home Depot.
How does all that work? Actually, better than the original roof-mount. We set it up just outside the screen at the end of our bunk on a lightweight sawhorse / campbox arrangement, and the cool breeze is just enough to make you reach for the sheet on even the warmest of nights.
Bottom line - Although we didn't reduce the gross weight of the Viking, we don't take them unless we expect we'll need them. When we do take them along, the A/C unit is easily stored inside when we're under way, and I rigged a generator caddy on the back bumper. Best part - I don't have to crank either of them up 10 feet into the air!
Oh, and at just over $350 total cash outlay, the whole transition was definitely a win-win.