They do not prohibit it.  They even recognize that sometimes code
requires it.

Don't do it "in the generator"  Do it external.

They do not tie them internal because it would violate codes when hooked
to house wiring where the ground and neutral are already tied together.
 Multiple grounds are prohibited because they cause ground loops.

Personally I would not bother.  Just recognize that the power monitor
can't work with a floating return.

Also recognize that if appliances in the RV are hooked to ground, the
GFCI in the RV will not perform unless the ground and neutral are tied
together.

Tom J wrote:

Why shouldn't they be tied together?

I have done it.  Some RVs have the ground and neutral tied together
inside the rig when being powered by a generator.

However, it really doesn't accomplish anything unless they make a good
earth connection as well which is not practical for most RV use.

A properly wired RV will open that connection when plugged into shore
power.   In that case the shore power provides the common ground and
neutral.

I have seen some that did not remove that connection and they pop the
GCFI on the shore power supply.  If tied together in the RV some of the
return current will flow on the ground line popping the shore power GCFI.

This is for Honda Commercial Generators but would be valid for all:

http://www.mayberrys.com/honda/generator/html/operation.htm

"Bonding the neutral wire to ground is required on some construction
sites. Honda’s Industrial Generators provide neutral bonding."

From a Forum:

http://www.campingworld.com/cforum/index.cfm/fuseaction/thread/tid/13722460.cfm
You bring up a good point. There are apparantly no existing standards in
the US on the grounding of portable generators. It is my understanding
that Honda generators have a "floating neutral" that is not bonded to
ground conductor. I have verified that my own EU1000 is unbonded.

<snip>
It is also my understanding that GFI recepticals on equipment powered by
such generators will not provide any protection.

Grounding of a portable generator in accordance with most electric codes
requires driving a 8' rod into the ground or bonding to an existing
grounding system. That is clearly not practical with portable generators
as we RVers use them.

I recently read a report of an instance where a person received an
electrical shock from a system powered by a Honda EU3000 generator. The
shock was caused by a faulty piece of electrical equipment but
reportedly would not have occured if the Honda had a bonded neutral.
<snip>