Depends on so many things. True composting toilet are expensive to buy. You be better off building an attached "outhouse" with a gasketed seat lid and a removable bucket that you can dust and dump into a long term container for composting. If you have plenty of rain you could build a gravity fed rainwater toilet with a simple septic system. If you have soft earth and temperate climate a mobile outhouse with a hole in the ground and sawdust or chalk works fine.