... this requires a lot of planning. ...
Yes, it does.
It might be helpful to know a bit more about you. Your English is very good but somehow I think you are not native to Britain. How old are you and your friend? Are you male or female? How much time have you spent camping and/or living in temporary shelters? What do you know about weather systems?
If your friend has so little life expectancy I wonder if a camp site in Cornwall is the ideal place to spend the next year. You probably haven't picked the best country in the world to do something like this, have you considered going somewhere with a milder climate? If your friend does not have a strong constitution, I would worry that her life might be significantly shortened if she had to spend an English winter in a tent. Others have mentioned that there might be limits on the length of time that you can stay at a camp site. Some of those limits are laid down by English law. The local government has obligations to ensure that people in its care are safe and healthy. A lot of the rules and regulations about living anywhere in England are designed to avoid many problems which you will encounter if you spend a year living in a tent. A comfortable environment for living does not just happen. It has to be made to happen. Things like clean water, places to prepare and cook food, dry bedding, safe sanitation and the disposal of refuse should not be taken for granted. It is almost impossible to keep everything dry when living in a tent in the UK in the winter. It isn't always easy in the summer.
When someone suggested a caravan, you said "We thought about a caravan but I someho find them rather repellent?" You did not say what your friend thought about them. That worries me. Does your friend like these ideas as much as you do?
The area that you are living in does sometimes have bad weather. For more than ten years I had a house in Plymouth and kept a boat on the coast, usually between the Tamar and Helford River. I miss the area quite a lot but I do not miss the weather there at all. I have lived (not just holidayed) in caravans for many years. My feeling is that for a year, a caravan would be a much more realistic option than a tent, even if you only use it as sleeping quarters and to shelter from very bad weather. You can put an awning or tarpaulins (or both) on a caravan, which increases the living space a great deal and in my opinion greatly adds to the habitability. If a caravan is out of the question then a van, the larger the better, might be an alternative for storage with a very little security and for emergency shelter. You can expect all sorts of things to be stolen if you leave them in a tent for a year. Even locked in a van they will not be particularly safe.
Any fabric will suffer badly from attack by sunlight and it is always at the mercy of the wind. If you buy a new tent, tarpaulin, awning or fabric shelter of good quality it might survive a year of sunlight or it might not. You need to check how the fabrics will perform with the manufacturer (NOT with the person who sells it to you, because they will most probably lie). Any fabric structure can be destroyed by the wind in a few minutes. The Cornish coast can see large storms which can last for days. If you only have a tent for shelter you will need to have an emergency plan in case the tent is destroyed by a storm. If you have an awning or tarpaulin on a caravan you need to be able to take it down to prevent its destruction by the weather. Obviously in any case you need to know about the weather. That means at the very least listening to the forecasts on the radio. It will help to learn about the typical weather systems that are experienced in the UK, and if you can understand the shipping forecasts, listen to them regularly (several times per day) and learn to use the information that will be a big help in your own weather forecasting.
