I too am running out of space in my house to store my bikes. I have three bikes inside my house and my 5 kids bikes are outside in a shed (which is also over crowded). My idea is to buy a 6X12 enclosed trailer to store our bikes and modify it to also be like a bike shop. We take our bikes everywhere. My concern though is keeping the bikes in an environment that is not controlled. Although they will be completely sealed off from rain, etc., they will still be exposed to varying temperatures and humidity. Does anyone think storing these bikes in a trailer is a good idea?
So long as the trailer is reasonably weather-tight it shouldn't be a problem. Since there's nothing in the trailer generating humidity, no significant condensation will occur, and, within reason, temperatures won't hurt bikes. (The only caveat would be that you maybe should have some vents that can be opened if temps rise above 90F or so, so that temps don't get over about 150F inside.)
It's definitely not as good as storing them in a climate controlled environment like your house but if you're buying a camper-style trailer it's going to be a little better than throwing them in a shed out back and a lot better than leaving them out in the elements. As long as the bikes are getting ridden and maintained regularly, normal wear and tear should catch up to them before the effects of the storage method you have in mind will. Unless you're running a climate controlled environment the two things you're going to have to watch out for are high humidity levels, high temperatures.
Unless you're running an AC or storing your bikes in a giant ammmo box, humidity is going to be a concern. Keep in mind that even if you don't have a steel framed bike, many of your components are either made of steel or have steel bits which are especially susceptible to corrosion. Even if the trailer is reasonably well sealed you may want to consider getting a chemical dehumidifier. These are often made of a type of clay or silica gel and you should be able to find them at your local hardware or home improvement store, or obviously online. If you find that they're getting used up faster than they should be then you probably have an issue with how well your trailer is sealed. Make sure to change the dehumidifier out as needed since the chemical type does get used up.
Regarding temperatures, extreme heat is the one you really need to watch out for. High temperatures won't affect the metal parts of your bike but they will degrade most anything made of plastic or rubber over time. Try to position the trailer somewhere that doesn't get much sun. If you live in an arid climate, consider venting it during the summer. However if you live in a humid climate leaving a vent open is probably just trading one problem for another. Cold shouldn't be much of an issue.
As an aside, don't store your bike in direct sunlight either. This is true of any storage method. The paint and/or anodization can fade over time which is purely aesthetic, but once again rubber and plastic parts (leather as well) are susceptible to degradation from sunlight. Hang curtains/towels/whatever in the windows of the trailer so that they absorb the harmful rays instead of your nice bikes.
I would suggest not sealing the trailer but leaving the vents open.A natural exchange of air will actually reduce condensation.Think in terms of an unheated crawl space in a home.If you close the trailer up on a warm humid day that humid air will form condensation the first time the inside of the trailer gets cold.Condensation will also occur if the trailer is cooled for several days and you open it to the weather on that first warm day.All that cold metal inside will not warm up as fast as the air.The warm and moister air will loose its water content as it comes in contact with the colder metal, again think cold beer, warm day,wet bottle.So basically allow the humidity to fluctuate with the ambient temp via ventilation.