Wheel base

I would always pick the model I could live that had the shortest possible rear overhang. IMHO a major drawback on longer C rigs. I also think that at the size you are considering your will be limiting your park access some and would be better off with an A.
By no means am I saying your choice is wrong. It just wouldn't be right for me.

OK, Apples to Apples then. Slides add weight, so it's possible Nexus used the 208 WB because of the big slide forward of the rear axle.

But Axle also means Wheel Wells, and I firmly believe styling takes precedence over engineering in some cases. The floor plan has to have places to hide those raised areas that break up the flat floor. So they hide the wheel wells under kitchen appliances, like our fridge, or the bathroom, like our shower pan. Pretty sure that's why there's a domed skylight over the shower, gives some headroom back.

So... Wheelbase affects weight distribution and weight distribution affects handling on the open road. You don't want to be rear heavy/front light. I doubt a 31-foot coach with 208 or more inches WB is going to have that problem. Many builders are now weighing each unit prior to shipment and including that on a sticker. I really wish they'd show Front and Rear, all Four Corners even better. Then you know weight distribution is right.

I've suggested that a test drive include a Travel Center (21st century political speak for Truck Stop) where you weigh the coach and then adjust tire pressure in all six according to axle weights using a tire manufacturer chart. It could easily change how the coach drives, and might bear on a purchase decision.

We are looking at the Phantom 31P, the super C is out of our price range.

The 31-foot Class C in my signature has a 218" wheelbase. The front axle has 4600 pounds front and 9300 rear. That's with no slides but fully loaded for travel with crew aboard.

A longer wheelbase shifts what would be rear axle loading to the front axle. If our wheelbase was say a foot shorter, it's likely the rear axle would be at, even over, full load. The Sunseekers have a max loaded weight of 14500 pounds, so FR is transferring some of the house weight to the front axle. Makes complete sense.

If the Nexus Phantom is the 32SC, it's a Super C with a max loaded weight of 19500. Also a much more robust chassis than an E450. Totally different animal than an ordinary C. Probably turns tighter, too, with a steeper steering "Cut."

The overall length differences are immaterial for going down the road and finding parking and buying gas and such. The wheelbase differences are unimportant for general maneuvering on the road, but they can affect the handling and general stability of the RV (longer wheelbase is nicer to drive down the road but does have a larger turning radius).

All other things being equal, I would prefer the longer wheelbase, even though it means a somewhat worse turning radius. It will generally make for better highway handling and weight distribution.

Typical Class C's are among the least maneuverable vehicles in parking lots and similar tight situations (including, perhaps ironically, some campgrounds). The turning radius of a stretched Ford E-series is not very good, and the long rear overhang makes for a good bit of tail swing. It's one of the compromises one has to evaluate. Still, there are not many situations where I've felt particularly hampered by the size of my (32' overall) class C. I would not care to drive through downtown Boston or Philly with it, granted; those are awfully good character building experiences even in a car. But most everywhere else the length isn't much if any trouble. (The width and height are more frequently concerning; particularly in construction zones, with Jersey barriers close in on both sides, it feels awfully wide!)

If you're intending to tow something, you want the longer wheelbase length and shorter rear overhang length.

Generally, motorhomes are typically built with the rear axle too far forward anyways (they extend the rear frame too far, rather than using a longer wheelbase chassis), so pick the longer wheelbase length, regardless of towing, and the motorhome will handle better on the road.

The only trade-off is that a longer wheelbase length makes for a larger turning radius when manuevering in tight places.

Eighteen inch difference in wheelbase matters more for maneuverability than an eight inch difference in overall length. But it doesn't matter all that much, my 29-footer with 190-inch wheelbase also needs to make wide turns, has a huge turning circle, and I have to watch what the rear end is doing on really tight turns. Even my standard length E-350 van with 158-inch wheelbase needs to turn wide. The E-series does not have a particularly sharp steering cut.

If what you need in a C takes you past 30 feet of length, you should be looking at short (26-32 feet) A-gassers, which will give you more living space for a given length, better maneuverability (more steering cut on F-53 than E-450), and usually at least a ton more chassis capacity (might be two to four tons, depending on which F-53 GVWR the manufacturer chose to use). Unless you need the overhead bunk, you will find the same space in a A-gasser can be about four feet shorter than in a C.

My driveway RV parking area kept me under 30 feet, and in a C that is almost overloaded when empty, but if I could have used a 30-32 footer it would have been an A (Sightseer or Hurricane were our top choices in 2005) which at the time were actually less expensive than comparable size C motorhomes.

For similar trim level, fittings, floorplans and costs as the Sunseeker, look at Forest River's FR3 series. Nexus does not build shorter A gas motorhomes, but you might look at Winnebago's Vista/Sunstar, Jayco's Alante, Thor's Ace, all in the Sunseeker's entry market category.