aquadd wrote:
What is a 16" center?

I guess my real question is "How do manufactured homes differ from
regular houses in terms of the amount of weight the floor can hold?" I
know regular houses can hold a 55 gallon tank easily, but are
manufactured trailor homes built to lower standards with regards to
the amount of weight they can hold?

Well, the answer to that is "it depends on your code". I am assuming from
your email address that you live in the USA. Here is a link to the federal
standards for manufactured homes:

http://www.hud.gov/offices/hsg/sfh/mhs/mhshome.cfm

Your state may have additional standards. Try a Google search for
manufactured homes building code with restricting it to only sites from
your state (state postal initials.gov).