Yes there are two versions of this as stated. One White the other cream/ivory. To my knowledge the mobile home never had a plastic base. It’s interesting to note yours seems to be missing the top stripe. My version has two.
In 1982 the mobile home was converted into the NASA tracking vehicle and still retained it’s metal base.
Then for 1985 it was converted again into an airport foam monitor. Again it retained it’s metal base. It wasn’t until around 1988/9 that the base was changed to plastic.