Gerald55 wrote:
To clarify, this is about the permanent installation of an inverter in an inaccessible location, and it should be wired into the 120V system permanently.
So solutions like plugging the inverter into the shore power outlet don't work since, well, that's outside and can't be a permanent thing. Similarly for only plugging devices into the inverter as I need them (the inverter is not accessible).
Suicide cord will work, and the risk of being electrocuted will be high.
Plugging inverter into shore power outlet with a shore power cord and cheap Female30A/Male15A adapter will also work and will be "permanent" for the duration of your stay, until you disconnect it. The hazard to you will be minimal, but you need to remember to temporary disable the converter and all the permanently wired 120V appliances like A/C and water heater. There still remains hazard to converter, inverter and batteries if you forget to disable something.
I don't think you've done your math yet. 400W inverter that you have, is fine for everything except few loads like microwave, and for those loads 1500W will be marginal. Get 2000W. 400W inverter doesn't need to be wired with short and beefy cable or mounted directly onto the battery.
I think all big inverters will have fan running as long as there is any load at all. You mount it where you can't hear it, and use a remote on-off switch. Inverters under 500W either don't have a fan, or you can get a 200-300W one that doesn't, and keep it accesible - for small loads this will be enough.