Timing the Purchase for a last-year's model

Some dealers are a little more willing to discount further between Christmas and New Years when their sales lots are almost vacant and they are looking to make their end of year sales goals. Paying cash is also a proven tool to help get the best price.
As suggested above, I would guess that the dealer will want some type of address for the registration/tag. This is something you want to establish before you try to close the sale on an RV.