We plan to use the Brittany Ferry on a weekday in May, two of us traveling by foot with a carry on bag each. Our thought is to train down from London the day before and book the ferry for the next day then, as well as our return trip which would be on a Saturday, possibly by the high speed ferry. Does this sound OK or must we book online in advance? A "convenience" fee is added if one doesn't have a UK debit card which we certainly don't have here in the USA. Also -- any recommendations for a place to stay in Portsmouth for the one night? The reviews for the Travelodge near the ferry sound pretty bad. Thanks!