The better canning jars are the screw lid jars. If you want IM me and will send our phone
number as we are also in the UK. Will gladly help you get through the fright of learning
to do it right (not as hard as a lot of folks want to make it seem).
I would not suggest canning on the boat unless you are having a day of very calm weather
and everything is able to be prepared and ready to go. Difficult to do for various reasons. On the other hand canning does let you make your own sauce style and have it on hand instead of making it from scratch (used to do alot of soups and sauces a few years ago).
Also the Italian pressure cooker we use has a name similar to "aenterum" Works wonders and since you are in the UK have some friends in Italy
that might be able to get you one and ship it up. Ours has two thermo plastic handles on the side and a central locking handle with a pressure safety
lock (impossible to open when under pressure). The lid is pressed up during function making it near impossible for there to be a leak (would have to come through the release valve or the safety
valve for it to happen).
Hope this helps and take care. If you want any recipes
let us know and will gladly give you some. By the way what part of the UK are you in?