Right in the middle of doing exactly what you're talking about. I went with a 8.5x18 flat front.
Yes to: radial tires, rear ramp door, RV style side door, multiple roof vents pre-wired for A/C, stand-up headroom plus at least 3", extended tongue, insulated ceiling with white vinyl finish, side windows.
No to: V-Nose, beavertail, heavy duty rear ramp door, torsion axles, 3/4" plywood on walls, factory option water system.
If you disagree with me about the above that's fine. However, if you are going to go for the factory packages then I very strongly recommend that you download some free CAD program and spend the time to design your floorplan VERY carefully. I can't stress that enough. Account for every inch of space. If you are going 8.5 foot wide then find out where the wheelwells are going to be in the interior space.
Then, when you go to specify what you want the factory to do for you, be absolutely SURE that you HAVE IN WRITING EVERY DETAIL. I don't care if the contract is 5 pages long, get every detail in there. Exactly where everything is to be installed and even exact part/model numbers if you can.
Stuff like, is the water pump 12vdc or 110vac, is the hot water heater 110vac or LP gas, exactly where is the fresh water tank going to go, black tank, gray tank, etc. Things that are very obvious to you but don't get written down WILL become a mistake. Ask me how I know.
Last, when you get your floorplan figured out, show it to a couple of people that understand the general idea of what you're trying to do, preferrably other competitors that you trust. Every question they ask should be a red flag to you that your drawing isn't clear enough. Make the changes to add the detail to make it clear before you place the order for the trailer.
Don't mean to rant on this but I don't want to see other people make the same mistakes I did.
Russ