Hi There,
Yes a service door would be required for installation of this cassette toilet.
Thetford recommend their Service Door Model 3 that comes in white or black.
You can find them for purchase at the below links:
https://www.mygenerator.com.au/thetford-service-door-model-3-white.html
https://www.mygenerator.com.au/thetford-service-door-model-3-black.html