Could be the answer is in the water heater you have. Does it
 have an AC heat element as well as the LP gas? If not, add
it and you will have a much faster recovery water heater.
If that did not do it, I would consider holding some RV
hygiene classes for your wife.

Of course, you can always save water by showering together.

George

Mark Jones suggested a flow-through hot water heater, which I thought was a
great idea and also considered early on.  There are both electric and gas
(convertible to propane) models available, but each has a separate
significant issue.

With gas, the concern is venting.  The coach manufacturer - believe it or
not - goes to a lot of trouble to determine where and how to vent propane
appliances, with the cooktop being the more or less notable exception.  I
would be very concerned about trying mount something that uses propane at a
higher rate than anything else on board and trying to find a way to vent it.

Electric flow-through heaters are much more common, but come complete with
the RVer's nemesis... high electric consumption.  Although these units are
extremely efficient, especially compared to standard residential heaters,
the energy demand is almost unbelievable.  Even a bare bones 2 gpm system
will draw nearly 50 amps at 240 volts.  In terms of power, that's somewhat
over 10 KW.

There were other posts suggesting converting the propane-only tank, which
does have a pretty rapid recovery, to combined electric/propane, but I think
the 10 gallon volume still remains an issue.  While I appeciate posters'
comments on hygenic behavioral modification and romantic opportunties, the
additional electric tank still appears to be the frontrunner in providing
desired volume.

Increasing volume does appear to be desirable to several folks who replied
to the original posting, so if something interesting pops up as a
suggestion, I'll sent it along.

Sincere thanks to the many people who took time to reply!
_________________________

Huh?  Make her responsible for HAULING the water and filling the tank to
achieve self-imposed conservation.  No water hookup allowed.

That would do it for MY wife.

I may have missed something but I don't recall this possibility:

Add a SECOND, propane-fired, 10-gallon, RV water heater.

This would be a perfectly do-able thing (CO$T is no object, I assume) and
would DOUBLE the amount of *HOT* water available.

It is beyond my plumbing knowledge to adequately explain here how the two
heaters are linked, but I know it is quite do-able if uncommon in an RV.

Ah, the dreaded Error 404...

Yep, unlimited hot water. For only $7,400 (the Monaco price for the
Hydro-hot option).

To install the Hydro-hot is a major project, not to mention expensive.
It is a complete heating system. We have had the Aqua Hot in the past
two coaches and the current coach has the Hydro-hot. It is a great
system but not recommended for a retro fit.  Best to educate the wife
on the need to conserve the hot water or just get used to cold
showers.

George