We see a lot of ovens that are cracked at the base after customers have placed aluminium foil there to prevent the oven floor getting dirty. Sometimes the foil has even congealed into the base of the oven and cannot be removed. We do not believe it is a good idea to place foil at the base of the oven as this prevents the heat from escaping and can cause the base of the oven to crack. The heat from the elements needs to bounce off the enamel and around the oven but cannot do so because of the foil. The trapped heat can crack the enamel and the end result can be very unsightly.
If you are going to use aluminium foil then the next best option would be to place it over the bottom shelf as protector. Oven Ready advise that you should use PTFE (Teflon) to protect the base of your oven. Some supermarkets used to sell it in a roll for £2.99 however we have not seen it on the shelves for a while so you may have to pay upto £10 per sheet online or buy from a hardware store.