The "danger" in having the neutral and the ground connected to each other in more than one place is in that this set up a "parallel path." That is, part of the ground wire will always be carrying current- which it is not intended to do.
In a mobile home, connected by a cable, the risk is a lot less than, say, in a situation where a section of conduit becomes a "neutral;" but it is still aviolation.
Connect ("bond") the two once- preferably at the point where the utility neutral goes one way, and the wire to the ground rod goes the other.
As to things "always being done...." well, trailer/RV parks are famous for incorrect wiring methods.
