I think we're making this more complicated than it is. I've kept my bikes (five steel, one aluminum) under a patio cover, open on all sides, for years. We have major winds around here much of the year, and all of them have been soaked many times. None shows major damage, even the 1983 steel Trek I bought used and made into a singlespeed.
Lube everything that needs it, and keep it lubed. Steel frames can be treated with Frame Savr or some similar stuff (linseed oil works, and it's cheaper). A plastic tarp properly tied down will protect them from nearly everything (leave it open a few inches at the bottom so condensation can evaporate). With a couple of pieces of plywood and some 2x2s for framing, you could build a little shed against the wall of your house, under the eaves on the lee side, if you're not living in a rental. Plastic storage sheds, the little cheap ones, cost only a few hundred dollars. There are all kinds of racks that will get the bikes up out of the way against a little-used wall in a bedroom or den. A tarp nailed at the top to an outside wall, so it hangs down over the bikes, with a piece of pipe or length of board screwed to the bottom, would cover them and stay in place.
Additionally, aluminum won't rust, and most components these days aren't steel. My old (now gone) Bridgestone MB lived three blocks from the ocean for almost five years, in heavy salt air, and the only rust was on paint chips I neglected and a few fasteners that had the plating scraped off.