Thanks for your suggestions. I have some really big dry bags, but I don't trust them very much. A marine roof box would be better. Or a big "banana case": http://www.google.com/search?q=banana+case
! Bikes are usually quite similar to each other so a few different "banana cases" would do for almost all bikes.
Actually one can google for "bike case" and get results like this: http://www.labicicletta.com/accessories ... -case.html
. But the case costs 1200 dollars and it still is not water proof!
Of course one could go for a cheap bike, but out of some different reasons I want an electric bike, and they sure are not cheap!