It's like any other business @Warren247 you need to research and develop a marketing plan to help you understand how best to market your business to those your market research has identified should be your target customer.
As part of your marketing you need to set up your own marketing channels such as social media and a website and invest in targeted advertising and PR to reach hosts and other potential customers.
You need to answer the question what makes your products different/better to your many competitors before investing in any marketing.
Can I ask how you identified that the increase in booking you had was only due to installing hot tubs. With marketing it's usually difficult to isolate an increase in demand purely down to one factor unless you do split testing.
(marketing and comms is my day job 🙂 )