Can I add foam board insulation to my tiny house to increase energy efficiency?
Although it can' t answer the question for the best solution,
a fast and easy method for simulation is offered on the site
www.ubakus.com.
The very important parameters dew points,  moisture and drying time can be seen in seconds, thus disclosing any critical layer combination that could effect the health and damage the walls.
R value, phase shifting and more are also calculated and displayed.
Best way is to open an example and change/add layers. Each layer can be easily switched on/off to instantly see any change. Toggling  between R- value/U- value is done by clicking on the tool icon next to the result.
It is free for private use.