Here is how I handle my mobile/portable operations. I applied to Lotw for two additional certificates, one for KC3EF/M and one for KC3EF/P. When I operate from a grid, I make sure to note in my log what grid I am in. Sometimes being mobile that can be a challenge especially if you are in a small corner of the grid. When I get ready to send the qso's to Lotw I create a adif for that grid and save it to my mobile log directory. I create a Lotw station location for that grid. If mobile I usually don't do counties unless in some place in the West where the counties are large. I then up load using my /M certificate. I save the adifs based on the trip so if I have to go back and correct something I can. I do basically the same for portable operations. The only downside I have found is I have not been able to automatically load back from Lotw into my logging program, since the /M & /P certificates are sub-sets of my main certificate. I usually go to the my Lotw account and manually select that the contact has been confirmed. Usually not a problem since don't make hundreds of contacts. After a bit I delete the station location unless its some place we go to frequently.
This is fairly easy to do in Lotw, but eQsl is another matter. It does not lend itself to setting up temp locations. So I usually upload to my main account and put in the comments what grid I was in during the contact. At one time eQsl was going to make this easier, but never seems to have happened.
My thoughts and this is what works for me. Takes some time, but it is nice to be able to help fellow 070 members get some of the more rare grids.
Dick - KC3EF