Rory,
there are a number of different solutions I was lucky when renovating to get access to cheap storage on a farm then able to move to free storage at my parents, others have built sheds in the garden, Trevor Thompson (T10) has a purpose built boathouse in place of the garage. I’d considered a boat tent from dancover, the most important thing is that the storage is big enough to allow you to work on the boat easily especially in poor weather as this is probably the time when you’ll be able to get away from the family or won’t want to be doing something else.