"F-350" doesn't tell us much. Older 460 or 351? Older 7.3L? Newer 5.4L, 6.8L? 6.0PSD? What type servity factor?
Regarding the filters, two parallel full flow filters likely would last about 20k miles, because conceptually a single good quality filter such as Wix could probably go 10k miles. Since the incident rate is cut in 1/2 per filter when you double the quantity, it's plausible. The question really becomes not so much about the fitlers, but can the oil last that long? If dino, I rather doubt it. If synthetic, it's possible.
One downside is that (with any ancilary system), you've got extra plumbing, etc to deal with. More hoses and hose clamps means more ability to leak or fail.
The upside to this type system is that, after the initial purchse, you'd still be able to get decent quality, inexpensive filters. With a true bypass system you end up with proprietary filter elements that cost a great deal. You probably won't like a TP bypass filter, as they are maintenance intensive; ruled out by your desire to not OCI in winter. But a dual full flow is cheap after the initial cost. Increases the sump size too, which slows maturity and adds to cooling affect (can be both bad and good, depending upon point of view).
What about a EaO filter? I realize that they are not warranted with anything but their own brand for the 25k miles, but they could possibly fill the need.
I guess that you'd be best off experimenting, and letting us know the results. I don't think that there is any clear-cut "best" choice here. Some amount of tinkering and value-driven decisions are going to have to be made by you. Heck, we'd all like bypass-filter results from full-flow fitler systems, but (at least at this point in the lubricant world), you can't get there from here. Somewhere along the way, you're going to have to pay the piper.
I see several options:
1) change oil 2x a year at 10k mile intervals (spring/fall = winter avoided) with quality synthetic and filter
2) change oil 1x a year with high end synthetic/filter (most notably Amsoil due to their paired product warranty)
3) run a multi-full-flow-filter set up, and do UOAs, probably with synthetics
4) run bypass with UOAs, likely with synthetics
I highly suspect that if you want extended drains, you're going to have to get into the paired Asmoil products for their warranty, or go with a bypass system.