We want to combine a day trip to Giverny and Rouen in the same day but aren't sure about arranging transportation from Paris. We will make sure not to go on a strike day. Also have heard about small guided tours using a van for maximum of 8 people. Not sure what the best way to go is-- whether to have the comfort of a guided tour (let them do all the arrangements) or the freedom of going on our own. We definitely want to get there early -- at opening.
I did them both in one day a few years ago - they are on the same train line so it is logistically pretty simple (unless there isn't a strike!). You'll actually take the train to the town of Vernon from Paris and take a shuttle bus from there to Giverny (lots of tourists, easy to find and follow, have cash to buy a ticket from the driver). Just know the schedules ahead of time and base your itinerary on that. You can buy tickets from the agent at the station (in case say you want to wait to figure out how much time to spend at Giverny, then head to Rouen when you are done), but don't cut it too close at Vernon station (the buses back to Vernon can take a while; you can actually walk back I think though I don't recall if I did or not).