Hi,
If you don't need to power everything, you could just plug only those devices you want to power directly into the inverter (or a extension cord that is plugged into the inverter).
If you want to have all outlets operated by the inverter, then you can plug your shore power cord (via adapter) directly into the inverter. Remember though, while everything will have power, you probably won't be able to run everything. Also, you will need to disable your charger (aka, converter).
Mount the inverter as close to the batteries as possible and use short / fat wires to connect it (don't forget to also fuse it).
Lots of inverters to choose from. Here is one source
Don Rowe.