There are some great ideas, although many would need a good amount of business acumen, cost and time invested.
If you don't want too much traffic car and caravan storage would be the best solution. The cars are likely to be show cars or investments that a rarely driven, and caravan owners will likely turn up a 2-3 times per year. Easy money for providing dry and secure space. It's not going to be the most lucrative business but it'll cover maintenance of the property and a bit of additional income.