Above would be my first recommendation. With a caution:
Have not seen ANY collaboration of that project, everybody references it.
Checking the math suggest it's not right. Freezer insulation is a little over twice as thick, heat loss should only be cut to 1/2, 0.1Kwhr/day is better than a 5:1 improvement.
Did not consider the size of it in my comments above. Someday.

If this is a one day party then buy lots of ice and many coolers.
MUCH, MUCH ... MUCH cheaper.
Or a quiet generator with a long cord to keep noise away and/or a big muffler.

If solar fridge is a requirement then:
Buy the best fridge of size you need. Often times the best is not cost effective.
Study it, see if you can add several inches of foam insulation all over.
If fridge is in the sun, cover it with reflective mylar or something like it.
Make sure it has good air flow around the heat exchanger.
Most have the heat exchanger on the bottom leaving the sides/front/top/back free to add foam.
Make it look nice!-)

For Power use two inverters.
Inverter sized to start motor has large quiescent running currents. (7X should do it.)
Split the wiring between control and motor, small inverter on control, large inverter turns on only when the motor needs to run. Many inverters have on/off switch, connect to this. Ask for help...
The large inverter quiescent currents can equal the motor running currents in one day.
Pick out the equipment I will show you the math. (if somebody doesn't beat me to it:-)

Calculated the energy cost to open a 24 cuft fridge/freezer with 15 cuft fridge area is 2.4 watts at 34F in 72F room. Door open 30 sec to 1 minute.

Let us know what you did!