[Avodah] Parsha Questions - Ki Seitzei

[SBA]

For those who may be learning this weeks parsha...

23:9. Rashi dh "Banim: "...lomadto shehamachti le'adam kasha 
lo min hahorgoy.."
Thus Amon uMoav who were machti the Bnei Yisroel are assur lavo 
bakohol.

AFAIK, none of the classics seem to mention where/when did
 Amon machti the BY?
(The Shaarei Aharon quotes a Sifri that they were advisors to 
the Bnos Midyon parsha.)

23:10/11. Rashi dh: 'Veyotzo' and 'Lo Yovoy' writes that a 
baal keri who leaves the machneh and doesn't come inside - is
mekayem a Mitzvas Asei and a Lo Sasei.

Isn't it a bit strange that these mitzvos are limited to Baalei Keri ???
(Although I did see mentioned that the same refers to a man and woman
 who had relations. But that would hardly happen in an army camp.)

And Rashi's comment that the BK is forbidden to enter Machne Leviyeh and 
Machneh Shechina also could do with some explanation.
Did such Machnos exist in the army camps? 
The Shaarei Aharon mentions that the Aron Hakodesh which went to war 
with them was the Machneh Shechina, which IMHO doesn't really explain.
Also, then what was the Machneh Leviyeh?

In p. 13 dh "Mechutz lamachneh" - Rashi writes Chutz l'anan'. Was there an 
'anan' in the army camps?
I saw one peirush say that although the anan disappeared after the passing 
of Aharon, it came back to them later bizchus Moshe. 

Has anyone any more/better explanation? 

SBA