The wooden platform is where the inverter, the box that switches between the inverter provided power or shore/generator power, and a electrical junction box are mounted. I am guessing that they are mounted on a platform because there is plumbing and electrical in the same compartment. If you happen to get a water leak it would be better to have the electrical components elevated.
The attached photo is a better view of what is mounted on the platform.
Wayne & Pat
2014 Georgetown 328TS
2013 Chevy Sonic Hatchback