Welcome DeeSee and congrats on your new T-320 SR!.
Does yours have the bunks in the back or no bunks and the monster bathroom along the back wall? They made 2 versions.
On the holding tanks, I just answered this for another member today. See here is will show you how to find out what your water system has in capacity.
https://www.sunlineclub.com/forums/f...ies-20446.html
The water heater, yours "should" be a combo gas and electric model. But... the 2003's sort of hid where the switch is for the electric version. There is 2 ways you can confirm that you have the combo unit, in case someone changed it along the way.
1. Look in the power converter at the 120 VAC circuit breakers. All the way towards the end of the breakers, there would be a 15 amp circuit breaker labeled, water heater. Do not turn it on if there is no water in the heater as it will burn out the element. If it was not rewired, they would be the electric power that leads to a switch to turn the heater on. That switch might be on or off, so do not turn on the power until there is water in the heater and you figure out where the switch is.
2. Go outside, let the white cover down on the water heater, there should be an Atwood model number tag on the right side when facing the heater. Tell us the model number and we will decode it if it has the electric feature and what revision level you have to help better explain where the switch is to turn it on.
If the model number starts with GC6 XX-XX. The G is for Gas, the C is for combo gas and electric and the 6 is 6 gallons. If there is no C, then there is no combo mode. The X's are part of the revision levels and can help us, help you figure out how to turn on the electric portion.
A prior owner may have changed the heater from original with an updated unit, and since the revisions changed between 2003 to 2004, the way the electric turns on is very different. Rather then send you on the hunt for a switch that does not exist in the right spot, tell us the full model number and we can go from there.
On the model number, M-320 verses T-320 what's the difference? The official Sunline model number is, T-320 SR. T stands for travel trailer, 320 is the floor plan, and SR is stating it is slide room model.
The M-320 is something NADA came up with to list Sunline campers by. They did not follow the T - for travel trailer, F- for fifth wheel etc., they just stuck an M in the first letter. We really do not know why. Since NADA lists Sunlines by year, the M, or T or F really does not matter as they use M on everything. The model number does not repeat between a fifth wheel and a travel trailer so it really does not matter when looking up NADA information on their web site.
Hope this helps and have fun with your new Sunny!
John