To keep the M Type body rigid whilst I make the ash frame I have only cut the floor board around the gear box. I have now tried the prop shaft up to the car and it looks as though I don't need to extend the cut out much past the end of the box. Is this so? It will provide extra strength - especially if I don't cut the "mouse hole" in the semi vertical panel behind the seat base. If Mike Ellis is reading these from his workshop in the sky he will be interested to note I have used cushionfloor - the stuff you put on the kitchen floor - as padding under the fabric body. I am sticking the surface you normally walk on to the plywood. It goes on absolutely flat and totally obliterates any nails or joints and the cushion layer has just the correct level of softness to provide a padded look. It is possible to cover each side of the tail without any joins. I am sure Mike would have told me to leave the tile effect on the outside so I wouldn't need to fit the fabric covering.
Jan, My M has a flat floor (no tunnel) & a single piece seat cushion. It was like this when I bought it some 30 odd years ago. One day I might get around to making & fitting a tunnel, Steve Christie kindly sent me some photos of various cars so I could work out how the tunnel should be fitted. The biggest disadvantage of the flat floor is that when you go over a large bump the fabric u/j rubs, a bit disconcerning considering the closness of ones nether regions! My car has been doing it for so long it has worn through the floor & made itself a clearance hole. Problem solved.
The M type has two separate floorboards with a gap of approximately 3.5" for the prop to move through so the weight of passengers/full spring travel can be accommodated. The tunnel itself has a main inverted "U" shape with fabricated thin steel ends to fit around the fabric couplings. I can take phots if you wish. There is also a cut out for the battery box just ahead of the drivers squab. Later M's had separate seat squabs with a one piece back rest, I'm not sure about the earlier M's but I thought they were the same. (I know there are pre-production photos showed a one piece full width squab) Mike