Unless they've changed since my just before the market collapse factory visit, Newmar is pretty much hand building from middle range (e.g. DutchStar) on up, so custom equipment is not that much of a problem. Easy if it is something they regularly do, more effort if it is something they'll have to go looking for.
It is probably better to first talk to a factory sales rep, before ordering through the dealer, unless you have a salesman at the dealership willing to do the work for you. Not a lot of confidence on that. I've found that RV (and car and truck) sales people work a lot harder trying to sell you something from the lot, or at a regional dealer's lot, than they will putting together a special order. They have bills to pay, kids to feed, and what you can close on NOW is money to them NOW, not 3-6 months down the road when your special build comes in.
For you, what it means is that you also have to wait. This is a tricky time of year, close to the end of manufacture for 2014 model year, factory will be building 2015 examples for the Louisville show, then there may be a short overlap of both 2014 and 2015 production, but likely no 2015 brochures or sales information for consumers until after the new models are presented to dealers at the show.