Thanks x-trail for pointing me in the right direction, the method worked well in most aspects.
Shows up fine in BaseCamp after installing to the computer, in Mapsource however it does not work well.
When zooming in and out some of the roads shows and some disappeares randomly, maybe at tile borders.
When "merging" the two typ files I realized that I had chosen the same grmn_type key that was used in the FriPro4 map so I will have to change a couple of my choises.
I also changed the FID of the finished map (with GMTK) in order not to have problem with the installed FriPro4 in my computer. Now the maps can co-exist in the computer.
With MapInstall I produced a gmapsupp.img and it worked fine in my gpsmap 60CSx and 64s.

I will continue with the typ-ing and adjusting with this "workaround" solution, possibly trying to add more layers from the shape files to make a complete map. After working with the typ file for FriPro4 I can see that the producer has used grmn_type keys that does not exist in MPC as a selection and I am not sure that I can get all the effects I would like to have as tilted text etc.