For such a short length, the standard Automotive 4 gauge cables from any Auto parts store will work fine. Even with the inverter the OP has.
If it makes one feel good to make a tiny, barely measureable improvement, then heavier custom cables can certainly be used. But the cost is a lot higher for the tiny unnoticeable gain.
I am not really a fan of solid connections. Though they are cheap and conduct well, the trade off (there always is one) is that they are not flexible. Road vibrations can cause stress on the battery posts. Over time this can cause problems such as a leak between the post and the battery case. IMO, a flexible connection such as a cable is the best for mobile applications. In fact a smaller gauge cable (so long as it is not too small) is slightly better in this regard as it will be more flexible than the expensive huge cables..
