If I were doing it, seeing as most park models use 2 50A inlets, I'd do the same thing. That way if you're in a location which provides that much power, you can take advantage of it. If you "only" have a single 50 amp service, then connect the two services together and you'll have to cut back on your useage, but it would probably still be sufficient for most cases.
The next buyer might want to park it at a location which provides dual 50A service, so having a single 50A connection might limit the appeal to potential buyers.
The cheapest and easiest time to do this is while you're building it.
I'd at least price out the difference between single and dual 50A connections.
I wouldn't even consider wiring it for 30A service.
Sounds like a neat project. I have a question, though. While you're building it, how do you make sure it's properly balanced so you have the correct percentage of weight (10-15%?) on the tongue? Or is this already calculated in the plans? Is a total weight also given in the plans? As mentioned above, what do you plan to use to tow this?
Good Luck.
~Rick