WDJ Ballast

Thank you, guys, for all the clever ideas you have come up with. I
only wish I had had my concerns earlier before narrowing and reducing
the number of alternatives. The access to the tanks is through
relatively small openings/doors under bunks and counter tops. I will
upload pictures to illustrate the situation better than I can
describe it.
I think I will stick to lead and see if I can fit a top to bolt down
and fill the voids in the tank with wood scrap. That will close the
compartment, secure the load, leave a flat surface on top and let the
ballast be removable.