movies in a rear facing car seat

My son is only 8 months old and he hates long car rides. We travel to see family at least twice a month which is a four hour drive. We are planning on getting him a more comfortable car seat, like a graco 4ever. We like that one because it last them through every stage, looks more comfortable than his carrier car seat and can rear-face a lot longer than most. Since we want to keep him rear-facing until at least 2, we also want a way to let him watch movies. I've tried letting him watch it on my small phone screen but I can't really afford storage for a full move, just YouTube videos. I've heard to get him the kindle kids tablet, but idk about giving my 8 year old a tablet. These tablets can strap to the seat, however, I don't feel safe with putting a portable DVD player/tablet on the seat in front of him.