Need portable system for camping

You are not going to have 14 hours of heavy sun a day.

You need to use "hours of full sun" for calcing your PV panels. The highest rating in the US is just over 7 hours in the southwest or southern Florida. It is only about 4.5 in the northern areas of the lower 48. These are the best figures for summertime. If you do winter camping, different figures must be used.

So, to provide 3600 watt hours a day, you would need 600-800 watts of PV panels.
You will also need a minimum of 600 Ah of batteries.
In addition to the inverter, you will also need a charge controller.

If you provide some more details, (what your 300W load for 12 hours is, what general area your camping is in, what months you camp, and what is the make and model of your innverter) more specific comments would be possible.