I also have a 70l plastic bucket to drop all the wet stuff, bags and helmets into to stop them rolling about
https://www.wickes.co.uk/Wickes-Strong-Flexible-Black-Mixing-Builders-Tub---73L/p/198840
Shower curtain in the boot. Cheap, waterproof and any colour you want.
https://www.roofbox.co.uk/car-boot-liners-mats/
Got one for both cars, rubbery material, with a lip and waterproof, neat and tidy, seem to have them to fit most cars, and much cheaper (and better) than manufacturer one in my case (VW).
Im thinking a Tarp cut to size and glued together might work now. Could maybe make a custom bike bag with that if its really dirty.
Mud, lost sweets, all mixed deep into the seats with a generous topping of spilled drinks and the odd vom*
If I was bothered about the interior of my car, I'd just fold up a tarp as appropriate, with some old towels/sheets to protect metal bits from each other.
*actually I think almost all of this has landed on the mud mats in the footwells or been caught in an appropriate container so far.
I use a picnic rug with a waterproof backing.
But are they actually waterproof or just water resistant? I used on on the backseats of my last car and put a wet tent ontop. The seats were soaked through when i got home.
