With diesel engines it is usually considered better to leave the engine off rather than turning it on for a short period. If you do want to exercise it then it is important to run it long enough so that it fully comes up to temperature. Unless you're prepared to take it for a drive that would necessitate quite a lengthy period of idling.
There have always been a couple different ways that folks go on this issue when it comes to diesel pushers. When I first purchased ours we sat in SW Florida for 4 months before hitting the road. A CG neighbor started his motor and generator (diesel) every month and let them run for 30 minutes. Another camper who owned/operated a towing company for big rigs let his DP sit for 5 months without starting anything. I found a couple other individuals who would take theirs out of the CG for a 10 or 20 miles drive in the middle of their winter stay.
I have always fell into the group that thinks it is better to take the rig out for a drive every couple of months if you are going to be sitting for 4 or 5 months. If you just start your engine and let it run you are not exercising the tranny, wheel bearings, brake drums, etc. I can usually find a reason for a drive, like going to get a recall taken care of some other maintenance/repair item done.
Diesels don’t need to be exercised and can be left to sit for quite a long time; certainly a lot longer than two months without any negative affects.
That said, you should be always be concerned with any storage about your fuel supply to make sure you have stabilizer/biocide/anti-gel as appropriate. Also, don’t forget that DEF has a short life-expectancy...some say around 6 months.
The same holds true about the generator diesel ENGINE. However, the reason that people advocate periodic running of the generator is to keep the stator dry and free of corrosion. This, of course, can be dependent on environmental conditions.