A Boring Dystopia

You're theoretically right about those examples. In a competitive market, the proprietor of some depreciating and universally available property with a finite useful life like a car renting it out to people who only need it for a short period of time isn't exploiting them. It's no more exploitative than selling them that car. In theory, the ability for a competitor to buy a car and rent it out for a competitive rate means that you can't exploit consumers in this industry. The profit would have to come from the labor power involved in the rental industry, like any other industry.

In practice you're describing an industry that is highly financialized and that operates inside imperialism, the highest stage of capitalism, where monopoly rents are the norm. So the rental company and Uhaul aren't making all their revenue out of the theoretically fair arrangement where their clients are essentially just paying off the depreciation and operational expenditure that goes into their property, they're also paying some ground rent or monopoly rent.