I've just done a 5 hour trip with my DD and found the dvd player invaluable. Definately kept her amused when she was a bit grizzly and she also fell asleep easier. Didn't even matter too much what we put on, we had garfield as well as some cheap kids cartoons from crazy clarks. We had borrowed ours from in laws and are definately going to buy one ourselves before next trip.
Mounting is easy if it comes with a kit, just slings over seat back. We did have to move the seat forward a bit as DD loved to kick the flap hanging closest to her. If no kit then on the centre console bit should do the trick, just angle it towards her.
The sound was fine, I ended up sticking my ipod in so that I could listen to music while I drove instead of sounds from a movie I couldn't see.
As for the glare, I used a cloth nappy over the window beside her. Depends on which side the sun is coming in.
Good luck