I think you'd be better off making it two separate wings.
You could design the struts like you've got, but if you go for the minimum wall thickness (2mm) then I'm afraid that they're going to break during post-processing or shipping. You may have to make them significantly thicker to survive post-processing, and that would hurt the look.
I had to thicken up the struts on this model quite a bit:
http://shpws.me/lp9l In that render, it looks pretty bad, but in real life, the whole wing is no more 1.5 inches wide and doesn't look too bad.
One small detail: on most biplanes, there were two struts on each side.. one forward, one toward the back.