For this week's iron craft, we were supposed to make something using a map. I happened to have some map fabric in my stash so I made some litter bags for Dean's car.
To make them, I made a large pocket and added some ribbon and D rings to them to attach them to the seats.
The one I made for the front seat, just has a short loop of ribbon since it doesn't have to go around a headrest.
To keep the bags from collapsing, I laminated 2 sheets of plastic laminate together. (11X17 size)
Then I just shoved that in with the liner...right inside the bag. That way, nothing gross will hit the fabric....even if it does, everything is washable.
BTW, I used some doggie bags as the liner (they come in a roll and attach to your leash for when you walk Fido and he does his business....yeah...those bags.) I think any of type of plastic bag would work though, just cut off the handle part.
If you are sure nothing gross will go into the litter bag, you don't even need a liner....but I'm not going to chance it...