I'm going to guess that this won't be a daily driver and that the unit as built is fairly heavy.
Also, IIRC, the V-10 Mod is inclined to consume oil.
If it were me, I'd go to the stash and give it either QTP or Chevron Supreme syn in the 10W-30 grade, or maybe Ultra 10W-30.
It won't hurt the engine at all to go a little thicker and might benefit it.
If you're going to have to go out and buy oil for it, then maybe M1 AFE 0W-30 and see how it goes with consumption.
If consumption seems high, you could always go with a thicker thirty or even a forty.
This engine would also be fine on any decent conventional 5W-20 or thicker.
That is what Ford originally recommended for it.
It's not as though you're going to put a ton of miles on a motor home and although you might run it during the winter, the engine will warm up quickly and stay that way all the way to south FL.