Honestly - go with the thick setup -on the model as you describe it -it is a far better approach
rigidity means far more than any "streamlining" on this type model
at 1360 sqinches -if you can do it for say 10 lbs -it will be a delight - after 12 lbs a nice sport flyer .
a 1.7" thick wing (lighter ) would be nice --but would require more rigging or some surface spars