Ford recommended a 5000 mile interval with the introduction of the Triton engines in the '90s, has since stretched it retroactively to 7500. This is using Ford-spec oils (their own is semi-synthetic) and filters. The "oil life" computation in my van will give me 8000-9000 miles the way I use the van, but I don't push past 7500, which is about 20% life left on the computer.
I'm rural, travel on the Plains and in the southwest, so most Ford dealers service trucks. The car vs truck dealership dichotomy is mostly in urban areas (where 90% of the customers live). On the other hand, nearest dealer might be 100-200 miles away, a different problem than finding out which dealer in a 15-30 mile radius is a truck dealear.
The self-change on the E-450 is easy. I still have my dealer do it, because he'll do the E-350 van for $9.95, the motorhome for $19.95 (plus disposal fees) and I can't buy the oil that cheaply.
I would not have the work done at a RV shop. Some won't even do it, others might do it but not necessarily use factory spec oils and filters, nor do the other chassis inspection stuff the dealers include in a cheap oil change to try to find additional services to sell.
If I didn't have a Ford truck dealer with such generous pricing, and didn't want to do the job myself, I would work with one of the local family-owned service shops I trust. I have at three choices with bays big enough, or at least willing to do the job on the ground, that I've been doing business with the past 30 years.
I'm wary of the franchised quick change places, even if they have a big bay with a pit (easiest way to do the job) because there just seems to be too much turnover. When a tech gets enough experience to get a better job, he'll leave for the better job.
Tom Test
Itasca Spirit 29B