An example for you, the Hartal door lock as fitted to Avondale, Elddis, etc caravans have keys WDxxx (3 digits). It is likely that the same coded lock barrel will be fitted to the lock(s) on the gas bottle locker, the battery box and the two key locks on the toilet and filler. I have 2 complete sets of keys that include hitch and wheel lock keys, but also have a WDxxx on my house/car keyring so I can enter the caravan without the 'full set' being used. This is handy at home but also on holiday where the full set can be left in the car glove box and the additional key used. These keys are available on Ebay around the £3.50 each so can be purchased while caravan dealers and stores are closed. You can buy a lock barrel and 2 keys with either a short 'tang' for lockers or long 'tang' for entry doors for £6.95. If you can find the key code in documentation then you have an easy answer!