My father owned a successful mobile home dealership for about 40 years. As a teenager, and later in college, I did grunt work (mostly manual labor) at the business in the summers.
Later, in my mid-thirties, I left corporate software development for six or seven years, and managed the business for my dad. While I was there I wrote software to help me manage things, which, after I left the business to return to software development, I turned into the SaaS product which I've sold to other dealerships.
I created a SaaS CRM/DMS for manufactured housing retailers ("mobile home" dealerships.) Monthly gross is about $4,000. Expenses other than my own time are $400 per month for the server. So about $3,600 a month net.
The MH industry contracted drastically after the 2008/2009 financial crisis, and the handful of dealership software companies still in the industry went under. So I basically have the market to myself right now. The total market is not very big, though - maybe 1,500 independent manufactured housing "street dealerships" in the USA at this point.
I have 15-ish paying customers right now. I'd love to be able to spend all my time on growing the business, but I've been too afraid to quit the other freelance dev work I do. Also, I unwisely took on a big contract that I haven't been able to finish in a timely manner, which is dragging me down. I wish I'd spent that time growing the MH SaaS instead.
I don't know about conditions anywhere in the world except the USA. But I've ridden across the USA, on different routes, multiple times.
When bicycle touring in this country, you don't usually (almost never, in my case) do bike touring on roads that carry heavy traffic. You ride on mostly empty roads that have very low traffic counts. Every state compiles Average Annual Daily Traffic (AADT) statistics. There are roads where you might see one or two cars an hour.
Later, in my mid-thirties, I left corporate software development for six or seven years, and managed the business for my dad. While I was there I wrote software to help me manage things, which, after I left the business to return to software development, I turned into the SaaS product which I've sold to other dealerships.