Kon & Mr G – My limited understanding of the MX5 is that the outer panels do not form part of the monocoque.
I
think that is defined as the inner structure only, something like the first photo here:
http://www.roadster.blog/2015/06/mx-...ctiv-body.html
Can I suggest you ask this question on the Tribute sub-forum?
As I am pretty certain that none of the MX250 builders have needed to go down the IVA route.
Good luck, Paul.