Of course it's formally correct like this as the expression origins from italian:Dictionary: collo
In practice though, a package is never referred to as a kollo but the plural form is also used for the singular. Hence, a kolli, two kolli and so on...
Furthermore, the spelling is not really defined - I have seen any variation from coli, colli to koli, whereas colli and kolli are the most frequent..
So, IMO the entry should read as follows:
package (comm.) - das Kolli / Colli (from italian plural of collo)
I don't have any reference apart from my experience...
What do you think? Any one else who works in transport/logistics industry?