It is completely possible (as long as none of the add-ons are bunkers). All you have to change is the no. slots in the OverlordContain tag. If you did tht and it didnt work, post up ur code so we can take a look. There are so many things tht can go wrong with the overlord/helix logic (like I have on my BRDM-2, which still isn't fixed after about a month, so I'll use this opportunity to gain extra help-the thread is
HERE)