This is showed only on Colt. Slightly different chassis to ForFour.
If there is potential problem with steel chassis, nothing that my 500A welder can't solve.
If any of that will be problem I can offer quite cheap welding services around Heathrow where I live, as I am just amateur by had professional teachers for years and still weld at work from time to time. 500A welding gun can go up to 9mm into steel of penetration.