Your pretty close... except your gunna loose some eficiency in your extension cords, adaptors, inverters, and charge capacity of the battery.
The battery you show on your other post you can find a lot cheaper on EBAY. I use those batteries for my kids Power Wheels... Look here for a veriety of batteries for as cheap as i can find them.
http://stores.ebay.com/The-Battery-G...=p4634.c0.m322
Then you will need a 12v battery charger (try wallmart in the auto section for a $20 one) I suggest you dry run the lights at your house and see how long they run on one battery. You might need another battery, or need to charge it some time during the weekend.
Remember, if you plan to have electricity around "fluids", make sure you install some sort of safety protection. An inline 30amp fuse on the hot side before your inverter should work (and bring extra fuses incase you have a few accidents)
Please keep us posted how this turns out. I might be in the market to make one similar to this.
Can you post a picture of your AutoCad rendering? Would love to see that!
Also, where did you get the LED rope light?