So, I live on a small barge with three windows

[MADem]

5. How big are the windows? If they aren't too big, go on and buy one of those silver/gold thingies,

(you can often buy 'em on sale as "loss leaders" for a buck or two at hardware stores), get the biggest ones you can find for huge trucks, then cut the things to fit the windows--if they are small windows you will get two out of one bigass truck windshield cover.

But wait--those sea planes? What about 'em? Stick the silvery slices, cut to fit, in a pillowcase of your choosing--perhaps a design that matches your decor. Then "tailor" it to fit by either sewing it up to fit or tape it with Ye Olde Duct Tape on the side no one will see, and jam 'em up in the window opening, affixed however you can manage (hooks, perhaps, or shove the thing flush up against the window and tap in some fine finish nails to hold it in place, but you can still bend it and remove it?). You will still get the insulation effect and the pilots won't get blinded.

EDIT: If you need something bigger than a pillowcase, splurge and buy a sheet with a cool design on it, or some remnant fabric. Fashion your silver to fit the window, and wrap the whole mess in fabric, tape it up with your high quality duct tape (on the hidden side), and Bob's Yer Uncle--a few finish nails to hold the thing up there, or maybe a few velcro strips here and there, or maybe both, and you're in business!

I use one of those in a summer cottage where the sun came in a good sized (large truck windshield sized, pretty much) window MERCILESSLY and heated the attic to an unreasonable degree. Since we used the attic for sleeping, it could get shitty up there even with the windows open, fans a blowing, and a crossbreeze established.

I didn't even get fancy--just clipped the thing up in the "too damn sunny" window with a clothespin behind the existing curtains, closed the curtains so the uglyass thing was not visible, and that alone lowered the attic temp by an astounding twenty degrees.

In the winter, that same window helps to warm the place nicely, so the uglyass silver (which is now in summer sandwiched between curtains and a curtain liner) comes off and the curtain opened in the daytime to let the sunshine in!