First, you have to understand that all bases have non-denominational services all in ONE church (bldg.) The services for each religion are done in different schedules. During Hanukka, for example, you might find symbols related to that holiday. So, it is only obvious to have a Nativity scene during Christmas time.
The decor on base chapels is usually done by groups within the base community, such like the Officer's Wives Club, The Boys/Girls Scouts, or the Enlisted Wives Club. There is no funding for a Nativity scene, this stuff is done by people who feel the joy associated during this time of year,to put it simply... Or with the donations received by the Catholic, Baptist or any other Christian group. I'm sorry to tell you, but thesegroups are the majority in the military, although all other denominations are highly and equally respected.
An MOS is what you do (Military Occupational Specialty. So what you earn is pretty much based on who you are/what you do. The car that you normally drive is paid by you, the individual, even if you are a Chaplain. The Gov. provides official vehicles for high ranking officials on official bussiness, just like any corporation would. Chaplains are considered high ranking individuals as well, with all the priviliges that come with such job. These vehicles are ussually identified by small side flags that denote rank.
In my opinion, everyone enjoys the fruit of their efforts. You will too, some day.
I should have been a chaplain, man!