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Excellent posts by Neil and Ross. When I was doing my degree in British archaeology and ancient history, we were during my Anglo-Saxon year told not to get side-tracked with studies of King Arthur. The very mention of his name brought rolling eyes from the lecturer, a senior academic in the field. Arthur is just a cipher, a shadow that may, or may not have some vague basis in historical fact back in the obscure post-Roman period. However, to try to pin him, and the tales around him, to historical reality is akin to trying to touch a cloud. If there ever was any truth to the figure, it is so lost in time, that the tales surrounding him are virtually useless as a record of early Saxon history. He is as real as Beowulf or some of the colourful characters from Celtic mythology.
Arthur was not even mentioned in the Anglo-Saxon Chronicle, let alone the battle of Barham Down between Dover and Canterbury - as far as I know that doesn't pop up until that compendium of tales Malory's 'Le Morte d'Arthur' in about 1470. Indeed, I'm not sure how Gawaine came to be anachronistically buried in the late Saxon Church St. Mary in Castro or Arthur visited Dover Castle. There is no clear evidence for any early Saxon fortification there at all - it is possible the Iron Age fort ramparts could have been utilised then, but there is no evidence of any built Saxon structure prior to the (very late) Saxon church. Even if there was a Burgh there, any remains were probably destroyed when Henry II built the Keep.
I suppose there may be some value in promoting Arthur in the manner Canterbury has promoted Chaucer's tales, but to promote any Malory derived Arthurian connection to Dover as real history is, I'm afraid, a disservice to history. Still, myths and legends can make the cash flow and that's how Arthur should be approached if he is to be utilised.