Alfred, there has been a lot of discussion on this subject over the years, a
search of the archives will yield a lot of info.  To sum up:  Any Optima you
try to install will not fit standing up, it must be laid on its side (with
some cutting away of metal at the top of the battery box).  The Optima
yellow top/deep cycle is expensive, from two to three times the cost of a
stock Group 41 battery.
And the capacity of the stock battery will be greater than the Optima.
Several members have reported short life spans on the Optimas expecially
under heavy use.  A stock Group 41 from WalMart, with their replacement
policy, might be a better waly to go even if it has to be replaced in a year
or two.  Some list members have gone to a Group 91 battery (larger capacity
than a 41) and is supposed to fit.  The Odyssey battery mentioned in another
post in this thread is an even smaller capacity than the Optima.  And that
brings you to calculating how much power you will be pulling from the
inverter.  Then you can figure out how big a battery and inverter you will
need and how long you can run whatever you plan on plugging into the
inverter.