I'm building an HO Athearn heavyweight observation kit to serve as a stand-in for a business car.  I'm putting the semblance of an interior in the car, so the metal plate weights which come with the kit won't fit.  In looking at ideas for mounting weights, I see two obvious possibilities:

1) Add weight inside the coal bunker located at the middle of the car.  This is accessible from the interior of the car floor.  Space is limited, so these would likely have to be tungsten weights and even then, I might need to go to option 2) for a little more weight.  I'm wondering if car sag could be an issue - but that's just speculation.

2) Mount some steel weights at the top inside of the car along the clerestory.  These could be steel bar or rod stock and could run the full length of the car without interfering with the car interior.

Neither of these are ideal.  Option 1) is a challenge both because of limited volume to work with, and because then the weight is concentrated at the center of the car instead of being over the trucks.  Option 2) puts the weight high in the car which doesn't seem ideal (I think it would accentuate any wobble of the car when it is rolling), but it would allow me to take advantage of the inverted-"U" shape of Athearn car body casting to provide stiffness to carry the weight without sagging.

Do you have any "lessons learned" from a similar situation you encountered on what _not_ to do?

When all is said and done, this model is still an old Athearn kit and is best a stand-in for the prototype, so I don't want to commit an inordinate amount of time or money into a solution — like most modelers, I have a backlog of other projects where my time and hobby budget would be more well-spent.