Every Special Hobby Tempest I have seen finished has way too much anhedral on the wings - even the two in the competition at Telford. Learning from this, I have been taking steps along the way.
My lower wing section was also quite warped, so much so that part of it had snapped. This picture shows the wing clamped to a board with sections of sprue under the wing to give the right shape. Then I built on the wheel wells, adding some structural elements from plasticard, and bracing everything with short sections of sprue. Not pretty, but I reckon you could park a Sherman tank on that wing now (1/35 only, other tanks are available) without it bending.
Onwards and upwards,
Roger