Eurotunnel then Italian Lakes

We're planning our first motorhome trip abroad this year (Sept) with 2 dogs so intend to go via Eurotunnel. We don't want to be tied to a specific return date. I cannot understand why they do a £199 flexi ticket when presumably you could go online and just book a single return crossing when you need it for half the price? Have I missed something?

We quite like the look of the Italian lakes so any current advice on stop-overs, route and sites would be welcome.