On Class B and buying new. Agree it really depends upon the dealer and the specific unit he has in stock. Sometimes they just need to move a unit out. So I suspect that the right B at the right dealer, could be purchased for less then a special order.
That being said, I would go pick the specific B you want, maybe narrow it down to one or two specific models that you feel is what you want. Then only search and check into those.
You mentioned full time usage. And many do well in B's in full time usage. But playing devils advocate, and not knowing your budget range, I would recumbent maybe a Super B (Like Born Free.), or a Class C - as better option for full timing. For your desire to get into the smaller sites of say some national and state parks, a Class C would usually allow you to go anywhere a B would.
And I'll toss out another opinion, getting a used higher end low mileage Class C, and then adding a Service Warranty, could get you into a both a nicer/slightly larger unit for about the same price. Lazy Days are very popular and well respected (And used prices reflect this..) units, much more comfortable for full timing.
I'll stop here, but if you decide you might want to also consider the Super B's and or Class C's, you could start another thread for input from the gang.
And of course, if B is where you want to go, then Go For It!!!