I have a liner like that I use instead of baking paper/tin foil when cooking, baking & grilling (its a cheaper version I got from Sainsbury's years ago). I don't know about using it in the bottom of the oven all the time but it is a fab product, I stick it in the dishwasher after each use.
Have you tried oven pride for the cleaning? Or there is a van I see a lot around here from a company who come out and clean the oven for you.
I have tried oven pride, but it only worked (brilliantly I might add) for the oven grids. Is there another one that also cleans the bottom of the oven. I do not like the mister proper mousse, I find it hard to rince an feel like it leaves a smell onthe food for days .
I'm ashamed to say I can't answer that as the bottom of my oven is so grim I thought it might catch fire the other day . I get DH to deal with that sort of thing. I know that you can buy a tray to fit in the bottom of our oven to catch all the gunk, maybe we should....