This cannot be emphasised enough. I was in Morzine for 7 days, and during that time I saw the sun for a grand total of about 10 seconds.
+1. That sounds like my week there in July.......
I've just come back from two years in London with a few side trips to France and Belgium for cycling (7 & 9yo in tow). Tips might vary whether you're prefering to do more road or downhill, but here's what I can suggest.
- the weather could be anything. We went to Tour of Flanders both years: 2013 was 5deg and kind of unpleasant, 2013 was 15deg and quite nice (and Gent-Wevelgem the week earlier in 2013 was 23deg and BEAUTIFUL!).
- I know EuroStar does charge additional for bikes, or anything above normal suitcase size (just like an airline really). I would guess the French railway (SNCF) is the same but can't confirm.
- I hired a road bike in Morzine (carbon Giant Defy with Ultegra) for €220 for the week. Mtb started at €40/day, but the price comes down if you hire for a week. Unless you've got a bike you really want to take I'd suggest hiring.
- However, if this adds up to too much would you consider buying a bike (Canyon?) over there (perhaps ordering it beforehand and delivered to your accommodation?)
- We found some nice places on the continent through AirBNB, but don't book anything property that doesn't carry a photo of their bathroom. It could be WAAAAY smaller than you ever thought possible.
- I'll second someone elses comments about staying in old towns in Italy - if you can get your car in you won't be able to park it there. In Siena parking was €2/hr just outside the city walls, or €5/day at the bottom of the hill, but there is a bus. We insisted on accommodation with parking and caught the bus into the old town.
- If you do hire a car then look up insurance4carhire, which enables you to pay £40 for a years worth of car hire insurance excess coverage
- We had brand new hire cars in Italy & UK at the start of the summer season (April-May). They must turn their fleet over at the start of the summer.
Happy to help further if you think my experience lines up with what you were looking at doing.