Diapers are one of my favorite topics :)
Prefold diapers can work in the Sierra in August because things dry in a reasonable amount of time. We took about 1.5 days worth of diapers, a collapsible bucket, a small bottle of Dr. Bronner soap, cord for a clothesline, and mini clothspins from the craft store.
Pee diapers – rinsed in the bucket and then hung to dry.
Poop diapers – bury the poop and then wash in the bucket. This might take a couple of trips back to get fresh water. (latex gloves are nice if you are squeamish)
The fewer diapers you take, the more on top of washing & drying you have to be. It usually took about a day’s worth of sunshine to dry a prefold.The covers dry more quickly.
Prefolds are pretty bulky, but not that heavy. We have also used fuzzybunz and g-daipers with the reusable inserts. Both of these are a little bit more compact. Another option is to use disposables for night time if you are worried about leaking. They can be hung up to dry before you carry them out.
We found out that it gets a lot harder in October when things don’t dry as quickly and all of a sudden you are nearly out of diapers.
Is your 3.5 year old comfortable going both peeing & pooping outside? If not, I’d make sure and practice that in advance.
-Peter (busy chasing a 4.5 year old and a 2 year old)