I am not familiar with the 2007 Seneca 35gs, so if you can fill me in on a few items I may be able to give you some suggestions:
- Does the RV have an automatic transfer switch?
- If so, what are the specifications regarding loads?
- Is the existing inverter located by the media center or is it by the batteries?
- Can you determine the size of the existing cables that the inverter gets its 12VDC power from?
- Does the inverter automatically come on when the shore power is removed and the inverter switch is on? (If it does automatically come on, you have an automatic transfer switch)
Your current 400 watt inverter requires 33Amps under full load (400/12=33Amps). Not saying that you will be using the full 1000 Watts of the replacement inverter, 100% of the time, but for ease of mind that will be 83 Amps (1000/12=83Amps), and I can almost guarantee you that your current cable will not carry that much current for any length of time (safely).
I believe you will need to upgrade the 12VDC cables that feed your inverter to safely accept the increase in 12VDC power needed.
If I may suggest, get a "Kill a Watt" meter and plug it into your inverter and turn on all your things you use the inverter for. The reason I say this is that your inverter may have a problem and it is tripping before you even get to 400 watts. I just looked at my living room TV and the DVR is only using 157 watts as we speak. It will give you a better idea as to what size inverter you should purchase. You may only need to purchase a 600 watt inverter. If you do not want to get the meter, sit down and add up all the watts that each load uses before the inverter tripped.
just my thoughts,