Try to negotiate from a position of strength. Even something so simple as sitting across from them in their office puts you at a disadvantage. It seems to make them more in control of the dealings; YOU want to be in control. Put them on the defensive immediately.
I used to call a half dozen dealers, describe the exact car I wanted and tell each one that by the end of their business to call me with their BEST price. Tell them they won't get a chance to give a "better" BEST price later.
Then when the calls come in, take the lowest one and buy it.
This can make them cry: When I bought my last Cadillac I told them the absolute most I'd pay. The said absolutely NOT. I walked out.
Three hours later they called and said they accepted my price. I said fine bring the car and paper work to my house and we'd close the deal at my kitchen table. Said NOPE we can't do that. I hung up.
20 minutes later they showed up in my driveway with the car and the paperwork.
Sadly, you have to treat most of them like dirt. Don't ever let them think you REALLY want the unit. They are trained to spot this, and will use it against you.
I NEVER test drive a vehicle; that's simply a ploy to get you excited. Drives them totally bonkers when they can't get you in the vehicle. If you must test drive, do it AFTER you've settled on a price or even JUST before you write the check (or sign the loan papers). And when you DO test drive it, (in the case of a MH) Weigh it, weigh it WEIGH IT. It'l cost you 10 bux at a truck stop.
Above all don't be concerned about hurting their feelings; you are only a dollar sign to them.
These are Boowho's rules of hard-assed negotiations. YMMV.