Well I lived on a houseboat for years...there are lots of storage tricks, clever internal carpentry you can do on a boat etc but the biggest game changers are (1) smaller amounts of stuff and (2) a smaller and simpler lifestyle, to be honest.
You have to pare back your possessions to the truly barest minimum, never buying anything if you can borrow it or rent it, and simplifying our lives so we don't need to store things eg. no hobbies that require stuff or different clothing, no holidays that require equipment like camping or skiing, etc. For a while I had only 1 coat (a raincoat) and just wore layers underneath it for the winter, and 1 pair of shoes at home - trainers for the weekend and commuting, and then I had 1 pair at the office to change into (so no wellies, sandals, etc). I remember once we had to go to a wedding and I bought a dress and shoes from a charity shop and donated them straight back afterwards. We did regular small half-loads of washing as we didn't have many clothes eg. I had one week's worth of pants and socks and that was it.
We shopped for dinner almost every day on the way home so seldom had anything in the kitchen, tiny pantry so no Ottolenghi style recipes with 100 ingredients, couldn't do a weekly shop or buy in bulk as no space eg. you're not going to find room for a giant box of toilet rolls so we would never have more than 2 or 3 rolls in the bathroom. Cleaning was one "multipurpose" bio spray but that was fine as it was all going into our greywater tank through thin plastic pipes so we never used bleach.
I know one of our neighbours who downsized onto their boat did something quite clever (though needing iron determination) - they rented a storage facility for a year and moved onboard with one suitcase each as if they were moving into a holiday let for a week. Then when they needed things they'd go to the storage to get it, and at the end of the year, whatever was left in the storage facility got sold, donated or chucked.