Consider this for a while the floor is effectively the only diagonal that joins one side of the chassis to the other, ie the near side of BR12 to the offside of BR11. If you make the floor in 2 sections then there is not as much bracing as having it in one continuous piece. There's nothing wrong with making it in two sections if it's more cost effective you just need to weigh up the pros and cons of both. (disclaimer) The added tubes in red which I'd make 20x20 are what the one piece floor would do to the chassis in my mind, please bare in mind that this is only my opinion and I have no way of proving if it makes any difference what so ever.
