You will need to make sure that all your RV's electronics (CO alarm, radio circuit, fridge....) are ALL disconnected when you put it in storage. That 5 watts of charging power will only help if all are disconnected, the battery is FULLY charged and the sun is shining REAL bright. That 5 watts equates to .4 amps, so all the above have to be in place. If the battery is not fully charged odds are it will not be enough to put any charge back into it.
Be careful, as some of these inexpensive SOLAR panels do not have a charge controller and or a blocking diode so it is possible that when the sun goes down the panels become a load on the battery. I did not see any thing listed on the website. I doubt that a .4 amp would cause the battery to over charge, but you never know.
2013 Jayco Eagle 284BHS
250Watt Grape Solar Panel, MorningStar MPPT 60 Charge Controller
1500 Watt Ramsond PSI, 2 Trojan T145 Batteries (260Ah)
2 - AirSight Wireless IP Cameras (used as rear view cameras)
EnGenius WI-FI extender, D-Link wireless (n) modem
MagicJack Internet Phone
2012 Ford F150XLT, EcoBoost w/3.73
157" Wheel base, HD Towing Package
Our Solar Album http://www.jaycoowners.com/album.php?albumid=329