GMP unboxed number representation

[I am not on the GHC list, so replies please either cc hugs-bugs or me.] I am chatting with the GMP (GNU Multi-Precision number library) people about "unboxed" (no pointer) representations. What do you experts on such implementations think would be a suitable low-level GMP implementation; that is, that would make the use in say GHC easier? (As I think GHC uses GMP, I thought this might the right place to ask for an input). Hans Aberg