For a .25 size plane, you may be able to sheet the center of the wing (over or under the fuse) and not use sheeting along the front edge of the wing. However you will need to use 3/32 balsa sheet between the ribs from the upper spar to the lower spar. This will make an I beam like structure in the wing. I have done it with smaller planes up to .15 and it has worked fine. However with a .25 or .25FX you may get some flex or twist. It all depends on what kind of plane your building. Is it a slow one or a hot fast combat? Hot and fast would require stiffer and stronger.