Well Ive done it 2 ways. On my 4 *60 i took a piece of triangle balsa stock, wet it down real good and with the wing in place pinned the the balsa to the fuselage forming a fillet between the fuse and the wing. leave it there until dry then glue in place. Use syran wrap to keep the water off of the wing. while it dries.
The second way is to go ahead and cover the aircraft, wrap the wing in syran wrap. the put a bead of aquirium sealant on the fuse and bolt the wing in place. let dry 24 hours. then cut the access sealant off the fuse thus fills the gap the sealant is fuel proof and lasts a long time. just use caution you dont get the sealant where you dont want it.
gtood luck