Building a RMH into a new foundation.

This spring I'll be pouring an insulated slab foundation for a  14 by 64 mobile home I've purchased.
I want build into that a 6 ft wide Mass that will eventually go to a RMH that I will build into an attached mudroom.  Question is what should I be telling the concrete company to get this done? Should I have them attach an insulated trough that I'll fill in with something else? Or maybe just some rebar that I'll use as attachment points and build on top of it.
While I'm at it should I do anything to the trailer while I'm not living in it?
I appreciate any spoon feeding on the subject thank you.

Mike,

8" thick slab for the heater. Reinforced with 0.5" rebar grid 8" OC on the top and the bottom of the slab.
It will last. I would not make it thinner, even if it seems strong enough, or with less rebar, even if it seems strong enough. I saw bad foundations too many times, too thin and without proper reinforcement.