OK...found your battery....http://www.battery2000.com/2m1270.htm
It is a wet cell sealed type with a 73.5 amp hour capacity when new. You can use HALF this capacity...say 35 amp hours before you need to recharge. So now lets look at your usage.
Car stereo...uses 2 amps....lets say you listen 10 hours a day...20 amp hours.
light...1 amp....8 hours...8 amp hours
Cabin light 1 amp....6 hours....6 amp hours
And your daily total CONSERVATIVELY is 34 amp hours requiring you to completely recharge your battery each day.
So...if the sun does not shine or the wind does not blow...you are out of luck.
Alternatives...add more capacity in batteries...two group 31's would give you 3 days between recharges.
Get a small gas generator and use it to run your battery charger
If you stick with solar or wind options...you would need a 120watt solar panel to replace your usage on SUNNY days.
If you go with a wind generator...any decent one will supply all your needs IF the wind is over 10 knots.
900-1000Watt portable generator.... $500-700
120Watt solar panel+ regulator+ install $800
Windvane w/ regulator on stern pole installed $1500
2 Group 31 Deep Cycle Wet Cell Batteries...$300
Hope this helps!