You may not be getting past the salesman. The salesman wants to sell you something NOW. His commission may not be paid until the deal is closed, and his kids have to eat.
That being said, this time of year could be a bad time for ordering. Builds might be backlogged several weeks or more with outstanding orders, one of the parts shops or suppliers could be backed up building something else, or you might be wanting a model year no longer built.
You can get built what you want at some of the factory-direct sellers (though at least one will not stray from his own options list) if you are willing to wait for it to be built. This wait may be longer than for some of the larger manufacturers, or it might be shorter if they've already started on something that has not been pre-sold.
As someone mentioned, it is somewhat the same with ordering cars (and to some extent trucks) today, except that there is almost no custom building in that industry now (all options are in packages) other than for fleet customers. Many car dealers don't want the special order business, but will check the regional inventory to see how close they can get to what you want.
I don't think most RV manufacturers work on a regional inventory system, but talking with a Starcraft regional manager, I think that company at least will try to help you find which dealer has what.
Winnebago, in particular, does custom builds. There is a custom vehicles division to do the design and engineering. You might have to talk to them directly, then order through a cooperating dealer. Not all dealers are this cooperative, especially when starting on a project that may not be finished and paying off to them for two to six months. But I think you are talking about options on a standard model, rather than a custom build.
