I have been saying this for years: You can sleep comfortably in a two door! You figured it out perfectly: slide the front seat all the way up and sleep diagonally. I’m 6’3” and I get my best sleep in my two door; went camping last weekend just to get some rest. DeepSleep mattress is key.
The issue I focused on here is not how long it takes for the oil to degrade. I was thinking about your warranty. If you ever have a warrantable issue and it doesn’t go how you’d like, Ford will likely point to lack of maintenance and also ask if anyone supervised your work.