265/70/17, also have to fit a longer axle due to the offset
I have exactly the same situation with the same size tyres on the Monterey rims behind the Heaslip .
When I fit the Montey Rims and tyres I will be using a spacerwelded on the bottom face of the axle, so as to lift the hub centre, effectively 'lowering' the trailer relative to the wheel centre and returning the floor to the correct level.