Bulkhead on first with only the 1/4" fasteners along the front (toeboard) done up.

Then fit the body frame, make sure its bedded in on what ever you are putting between chassis and bodyframe

Then when the body frame to bulkhead join is as good as it can be and allowing for a bit of sealant between the bulkhead and bodyframe, fit the fasteners on the side of the bulkhead

Then fit the inner wings

Arwyn