Thanks for the input guys.

It is possible that I am overestimating the amount of rust that could be hiding down there. Currently the passenger side corner is looking pretty poor, with rust extending to the nearest vent flap hinge and there is a 20mm x 100mm hole in the passenger footwell (which should be an easy repair).

I may have to get out the grinder and try one of the repair panels as an interim solution. It sounds as though I wont have the time to perform a full swap out.