Mrsnonsmoker, there was a review on park homes on TV recently. You have to beware that buying and selling is usually through the park homes site owner, at a percentage cost. Also residents are expected to upgrade every 10 years or so. Sites may change ownership, and the terms under which you bought, may be changed, not always to your advantage. There may be restrictions on your visitors staying with you. Young children may not always be encouraged, as residents can be of a certain age, and expecting a quiet life. As to your wanting to be a seaside gran, your family may not be able to visit as often as you would like, as they get busy with their own lives.
Sorry to be a pessimist, but these are things to bear in mind. If the move suits you, go ahead and do it, and enjoy.