In reply to GaryK:
Me and the Misses recently stayed in Littlesea campsite (£16 per person per night) which is just up on the mainland and we had a lovely stay. We could park the car right next to the tent so our drive onto Portland each morning was easy.
We chose it because it had hot showers and proper toilets which none of the campsites on Portland seemed able to offer.
It also has a Papa John's, a Fish n Chip shop on site and a reasonably priced convenience store but it's also quiet enough over in the tent area that you can keep yourself to yourself and cook on the camp stove and watch the birds flying around the Fleet which is what we did.
Post edited at 16:06