Singular and plural chassis are spelled the same, but that doesn't make it right! I'm more inclined to spell it chassises personally.
Spelled the same, but pronounced differently: https://www.merriam-webster.com/dictionary/chassis
Chasses :-)
https://en.wiktionary.org/wiki/-sis
Chassis'
Spelled the same, but pronounced differently: https://www.merriam-webster.com/dictionary/chassis