If all you are talking about using it for is "charging cameras, laptops, etc", then why go for an inverter at all? What you're talking about is going...
12V DC -- (inverter) -> 240V AC -- (device charger) -> somewhere between 5V and 20V DC
Which is probably a good way of heating up the inside of your vehicle, but probably not of making your leisure battery last.
Why not just buy 12V chargers for the devices, and stick to a 12V power circuit in the vehicle?
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