I installed a similar system but didn't connect to all circuits. I only wanted 2 circuits to have power when my inverter was on. tv circuit and above the sink circuit. I used 2 x Xantrex 15 amp auto transfer switches ($60 ea) the were very easy to install.
Turn off all 110 power incoming to trailer- *** safety first
Identify which circuits u want power to
Remove factory 110 power cord from that circuit. I cut mine at the back of the converter and pull it out the front
Then attached the cord you just cut to the 110 side of the xantrex transfer switch
Attach the other input side to the power from your inverter
The third side (output) then goes through the back of the converter your picture showed and re attached to your original 110 breaker,
I did mine in about 1 hour.
Auto transfer switches for individual circuits 15 amp are way cheaper the whole rv switches.
I did mine this way so that there way no way any other devices (ie water heater) were trying to run on my batteries.
Hope,ths helps,