This the information I found for Rims for Ford F-350 2017
Bolt pattern 8x200
Width (inches): 6.5;
Offset (mm): 142.
Bolt pattern 8x170
Diameter: 17.0'' - 20.0'';
Width (inches): 7.5 - 8;
Offset (mm): 40.
Notice that the rims might be two bolt patterns, 8x200 or 8x170, and almost every dimension could vary. There seems to be no one 'stock' size for a F350.
I think that you should wait until the RV delivered to see what rims you have exactly. Those that carry a spare sometimes only carry a tire, they let a tire service mount it on the flat tire's rim. Unless you also carry the jack, jack stand, socket, and breaker bar long enough to remove and install the new tire, a tire service will be needed anyway. Carrying a tire insures that you'll have one 'in stock' when you need it.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI