I have a small 210UDS with a similar setup. There is storage under the dinette's slide bench seat. I think it would be more accessible to put in the hatch and get to it from outside. I researched it and found a source for the door/frame assembly. Then I thought about it - we store extra dry goods there: paper towels, plastic silverware, napkins, toilet paper, k-cups, etc. And it would probably be more inconvenient to have to go outside to get the items to restock. So-I ended up thinking it was a great idea - but . . . probably not?
2012 FunFinder X 210UDS
4-68 watt flexible panels; 1-215 glass panel/4 Battle Born LiFePO4 Deep Cycle Batteries
2014 Ford F350 6.7 Liter PowerStroke V-8 Diesel longbed, SRW