Side access outside doors are off the shelf items, some can be used as a hatch, check out marine suppliers.
If you plan ahead for your floor joist structure you can simply build a removal floor section, they have recessed thumb hole latches (marine item) or you can just cut an opening to pull the panel up and just cover that small opening with flooring you can pull up.
A friend has a small class A, the kick panel lifts up from a dinette seat exposing the edge of the floor and a strap, loop of material, is used to pull up the floor. The floor just lifts out, no hinge required.