I wouldn't recommend setting up a station location with a /P or /M after your callsign. That is going to cause issues with eqsl and LoTW mapping. Instead, when operating portable or mobile, do what you are currently doing, i.e. set up a station location with the information for the location you are running from, but leave the callsign unmodified. Instead make the appropriate setting in the M/P box (located directly under the Country setting). That setting will then be recorded in the "My M/P" field in your contacts table when you log a contact (you may have to enable that field under Edit/Contacts Table/Enable/Disable Columns). That way you can keep track of which contacts you made while operating away from your home location. Note that there are two M/P fields in the Contacts table, one called "M/P" which indicates the M/P status of the station you contacted, and one called "My M/P" which indicates your M/P status when you made the contact.
Anyway, the above is good general advice, regardless of what net you are participating in. As far as what counts towards club specific awards, e.g. 3905cc awards, that is something for which you would need to get help from the specific club from (either via their website or a knowledgeable club member). I do know that the 3905CC does have some very specific unique rules for their club relating to M/P status, because the M/P status functionality in NetLogger was added at their request, even though I think it is useful for all cases, just not necessarily as it might apply towards club awards.