I'm always build random things on Ryan's fleet builder (like everyone else) and came across something today that didn't work.
I took an Arquitnes and put Tua on it. It's a small ship so the wording at the bottom does not apply. I wanted to put 2 X RBD on it and turn it into a tank along with engine techs. After I picked the first RDB it was greyed out as an option.
Its not a mod or unique, so that should work right?