Hi I' probably over tinking this being an engineer.  

When it comes to sanding the vertical join of the tak lids (on any kit but mines' a wherry tandem) is it usual to leave the tank edge vertical/ 90 degrees  where it joins the angled bulkhead/ face to retain maximum thickness and strength,  or to sand the tank lid edge so it matches the angle of the tank wall/ bulkhead.  

I'm assuming the second option looks better once complete and am not sure it would really affect the strength.  

Thanks for any thoughts.