This is a common question - the answer is that nothing, ever is valued by some book. There are mobile homes all over the Country, all with different values.
Since their value is so dependent on where they are located, it is really up to how much someone is willing to actually pay for it.
If, however, the home is on a truck to be moved, there would be some value in it for sure. But this will change immediately when it is placed on a spot.
Finally, if the home value is desired specificially when the home is on the truck, then it will come down to a NADA guide value, along with condition, size, amenities, etc. etc.