no need to draw up anything.....just put a small 45 degree gusset in every 90 degree corner you see in that area...then assemble and glue in the fin and stab. 90 degree corners are weak points....you will have to work around some areas of the fit to get this done. like i said....if you think an area is weak....add a 45 degree gusset....or maybe 4 or 5....on that line. its all about support. the strongest ultralights i done machine work on for the stress load in sun and fun in florida were constructed from chrome moly tubing. we triangulated every possible weak joing that had a 90 degree corner. you get the strength from triangles.