Sorry but this is a myth. I open the bator during lockdown and have no problems at all. I candle unhatched eggs to see how they are doing, I take out hatched chicks and empty shells. I have never once had a shrink wrapped chick that resulted from this. Sure, you probably want to add some water...
Thats what is great about the Genesis. It adjusts the temp on its own. Mine hold temp just fine. I personally think a bator is the better way to go. Even with a Silkie they still have to go broody, you can't just give them eggs any day of the week though they do go broody more often than most...
The Hovabator Genesis is a good way to go. You can get one without the turner if you are on a tight budget. I have four of them and have very good hatches. Try ebay or incubatorwarehouse.com.
I have lots and lots of Marans (hatched 27 from DMRippy not too long ago), but I can sell you some Lav orps and I'll give you more Legbars to replace the clear ones if you'd like
I feel so out of sorts...cleaned out the bators a couple of weeks ago and then set 85+ eggs all at once, so I haven't had anything hatching or on lockdown for awhile now...and I'm having withdrawal! Next lockdown is coming up and it will be my first duck eggs...then all 80+ that are still in...
I hatch mine upright in egg cartons also, I do cut the sides down so that they are not too high so as to impede the emerging chick. I do not cut the bottoms out because I have found that with most eggs it is only a small part of the egg that is actually in contact with the surface of the carton...
I hope you are quarantining everything you bring in...many poultry diseases are impossible to get rid of and will require that you cull your entire flock if they get infected...
I hatch all of mine upright in egg cartons. I cut down the sides so they don't impede the chicks when they emerge. When I put the eggs in the hatcher, I candle to see where the low side of the air cell is, and I turn them all in the same direction that way they will all pip on the side facing me
I would recommend dry incubating your Marans. They are much harder to hatch at humidity levels people normally use. Keep your normal level for lockdown but you want it around 20% for the first 18 days.