This might help with the out-rigger issues
VOSA have provided the following response to your questions;
Q) What is classed as chassis? Is it purely the outer longitudinal rails or are the crossmembers between these also a part of the chassis?
A) Chassis should be taken to include crossmembers.
Q) We know that cutting or shortening a chassis is classed as modification but is this relative to the vehicle wheelbase i.e. the chassis must remain uncut between the 2 axles but anything forward of front or aft of rear suspension mounts can be removed?
A) Chassis includes the full original length of the longitudinal members including to the front of the front axle and to the rear of the rear axle.
Q) Is it acceptable to remove bodymounts, which contribute no strength to the chassis when changing a body to a different style /make?
A) Yes, providing they are additional to and are not an integral part of the chassis structure.
This little statement has helped me in the past but be polite when dealing with DVLA and always remember they are never "wrong" just "mistaken"