The circular stick on deflectors work fine on my Passat's plastic lights and the instructions cover just about every car so you'll get them in the right place easy enough. Clean the lens and warm them up on full beam for a couple of minutes and they'll stick fast. They're cleverly designed so you can't easily reuse them. The AA ones on Amazon can be had for much less than Halfords and other places.

Last year I was stopped and checked as I parked up at the Aire de la Baie de la Somme on the A16 45 minutes from Calais. They checked the deflectors asking for the lights to be switched on, checked for 2 hi viz jackets (keep these where you can reach them in the car, not the boot) and all paperwork including letter from the company authorising me to use the car abroad. They chose not to speak English but nevertheless all very amiable and courteous. Not worth the risk IMO of not having everything sorted before you set off.