I'm in the San Francisco Bay Area where most of our lot sizes are postage stamp size. I have a rental in Gilroy (South of San Jose) where some of the neighbors store their fifth wheels in their side yard but they end up dominating the appearance of their property. Not quite an eyesore but definitely just looks out of place. Having traveled a bit in the Midwest I'm envious of the lot sizes you have even within the city limits where building an out building isn't even a problem.
Even though I have a fiberglass camper (Bigfoot 10.6) that is better at outdoor storage than most, I looked for indoor storage specifically to be worry free. If it rains (becoming less of an occurrence in California with our perpetual drought) I'm not constantly worrying if my roof is leaking or not. I ended up finding an old manufacturing facility near Hollister (50 miles south of San Jose) that is converting to indoor RV storage. I pay about $225 a month to store a mini-van and my F350 with camper. Though the cost is high, the camper is primarily for business use so it's a business expensive that gets written off.
If I had the space on my own property I would take the money I'm spending in storage and invest that into a small shop / RV garage. Outdoor storage is rough on the RVs and if you factor in the additional wear and tear / maintenance and lower resale value for a weathered RV the spread in costs probably isn't that far apart.