Pirke
The DR400-140B & 160 are identical except for the fuel system both have the main take mounted in the centre section that holds 110 lt the 140B has another tank at the rear under the baggage bay that holds 50 lt. The 160 has in addition to the main tank two wing tanks that each hold 40 lt.
As to people stepping on the fabric, I have never had it in thirty years of DR400 ownership, the walkway structure extends a long way outside the anti- slip area as it does with most metal aircraft, step out side this area on any aircraft and you are into a repair that will probably cost more on a metal aircraft.
Maintenance of wood aircraft is less well known within the industry but the costs are usually slightly below metal aircraft.......... But not by much !