I have already put in my time off request for April but I can check on what my work has going on in March. I am leaning more towards the Barcelona to Venice because I will potentially be meeting up with someone in Italy to catch a train to Munich and stay with a family friend before heading back to London. I also want to see the ruins in Athens. I have two other people that may do the Barcelona to Venice cruise, but not confirmed.
You can find very cheap one-way airfare. Sometimes you can find a cheap train ride out of Venice to Milan (or another airport), then fly out. The options are amazing! Let me know if you need help finding airfare, I'm in charge of travel arrangements for the company and for my executives department. I have some handy tools and spreadsheets. Let me know.