Oh my nemesis the Sub wing! lol I completely scratch built mine on my new airplane. Those things are fragile and have a tendency not to last. Do whatever you can to divert overflow fuel away from it. Raw gas is even more caustic than raw glow fuel. Maybe at least consider using an overflow bottle when filling the tank.
fully sheeting that thing is not a bad idea. It will make it more durable, and the weight will be negligible. O made mine out of a foam core and vacuum bagged it with poplar sheeting and gorrilla glue. Has worked out great so far.