The gas smell will be your rear diff over heating and burning the diff oil. This is mainly caused by mismatched tyres and potentially VCU failure.
DO NOT DRIVE THE CAR UNTIL YOU HAVE CHECKED THIS AS IT WILL DESTROY THE REAR DIFF AND IRD!!!
How do i know about the gas smell?? I chucked some bags of rags out that i had moped up rear diff oil with from an overheated rear diff for the dustmen, later on that day a british gas man came round looking for a gas leak after numerous reports from the public!! The funny thing is, there is no gas in the town i live in, LOL!!!