The more the better if you plan on nixing the genset. We need on a sunny day about 100 watt panel to keep up. We went with 500 watt system though so we can get the equivalent of 100 watts on cloudy days. On sunny days we use the extra power to cook and run the fridge.
500 watt renogy MPPT CC. 425Ah trojan deep cycle battery bank. This has worked great for us over the last 8 months of living in our TC. We use the crock pot 2-3 times a week for cooking, make coffee every morning in out 110 coffee maker etc. If you want to run a swamp cooler (we have looked into this) and it is using 4.5 Amps + the pump draw you will want more than 200 watt system unless you can be in the sun all the time.
Remember there is inherent loss of efficiency at every step from wiring to sun angle to charge controller to batteries etc.
Go as big as you can fitting solar/ battery if you plan to use it to cool the camper, even with a swamp cooler.