Like Atomic suggested, we use high amperage relays to both reduce wire size for switch leg and to allow small switch rating for up to 40amp load. Great article on relays at this page
It helps too if we don't turn on the inverter-fed loads until after we turn on the inverter. We learned this the hard way. We failed a relay by switching the inverter with the inverter loaded, apparently fused or burned the contacts.
We similarly use a relay to control the feed circuit for two ham radios (25 amps), and added three switched relays in the truck, one each for the air horn solenoid, the air compressor, and an accessory circuit with ham radio and tire monitor. These are all small Bosch type relays, like the Hella ones.
One change we made, we soldered an IN4002 diode across the 12vdc control circuit terminals to serve as quenching diode or spike suppressor. Because we are serving costly electronics with the relay circuit, it just makes sense to put a $0.50 diode across the relay control terminals, unless you buy a relay with suppression already built-in.