NOW! And 2 schools of thought on your subject.
1st thought...That's what the fall RV shows all is all about IMO. Dealers have lots of "last year model" sitting in out back. At least at Tacoma dome every year and trying to get rid of them. Know your pricing well because somebody's got to eat the deprecation, even though the RV is "new" you don't want to be the one eating it.
2nd thought...We (I should say wife) kept her eye out for a good RV. Took several months but she got exactly what she wanted in floor plan and make. Many people buy when newest model comes out. Keep for only a year or 2 then upgrade. (Must be nice to have the $$$ to do that. I don't). Our RV was from a couple that traded in every other year and this was their 4th time. Sales guy knew it was coming in. Used about 6 times total in 2 years. Original batteries in TV remote, Stock goodyear marathons with tread depth was 98% (first thing we got rid of) under carriage paint (cheap oem paint, that they all put on) very little pitting from road debris.
Where ever you are looking at, your sales guy should know when somebody placed an order for a new one, waiting for new one to be delivered. Their trade in (or what is going to be their trade in) has probably already been looked at and sales probably knows when it will hit their lot, to be re-sold. And more importantly to you is the dealer has already beat the deprecation out of them. And is now marking it up to you. Dealers profit is in the middle, how much is up to you, so find a good one and go in knowing exactly what you want and what your getting. Then if RV pre-trips out 100%, get certified check from local branch and tow it home. Be ready to act. Not getting beat up on price of installing 5th wheel or wire this thing or wire that. Get fax number of dealer and have your insurance company fax binder to dealer or send to your phone before you tow home. All the other stuff you want to get to make rv better, you can get later and probably at better price.
Only down side I see is...even though you'll end up eating very little deprecation when you buy this way. There is still some downside. By this time next year you'll have a RV that is 3 years old. And don't expect any help from OEM or dealer when buying used. Which is OK with me, as they tend to do a hurry up job when fixing things anyways. 99% of stuff you can fix yourself. The other 1 percent, if there is any will still be less than warranty IMO.
That's what worked for us any ways. Wife probably spent couple hours on phone each week calling, to see if any of what she wanted were coming in.
Good luck. (you'll need it when they add tax and license)
OH... being you said 5th wheel. Make sure you have enough power to pull it. Don't run out of truck before you run out of pin weight.
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"