I just bought a new 2007 2120 SC and one of the issues I struggled with was having a marine head with a reasonably sized holding tank and macerator pump.
I thought the room is okay for the actual head and it would be simple to wire, but the spaces I saw for the holding tank were all too small for me. So I bought the standard portable head. They do have a pump out stem for them and a larger holding tank base so I may upgrade after this summer.
http://www.thetford.com/marine_series.cfm
I also studied using an expensive VacuFlush which olny uses a pint per flush thinking I could feed it with an antifreeze solution in the winter or year round and not have a water intake (I use my boat year round here) but lots of equipment to install and still neeed a holding tank.
Maybe after I first use and get used to emptying the portable, it will not seem like such a headache.
What did you decide or experience since your question?