We signed a paper called a "Buyer's Agreement" which specified what we were ordering, and the price we agreed to pay. We made a small deposit. That happened on July 22, 2010. That did not start the warranty clock.
The trailer arrived on the dealer lot on August 27, 2010. That did not start the warranty clock.
On September 1 we did the PDI. The dealer had a set of paperwork including a new version of the Buyer's Agreement showing the purchase date as September 1. Because we were going to title the trailer in another state, they also gave us the original title, with transfer information filled out on the back, showing the purchase date as September 1.
The dealer asked us to sign an acceptance letter agreeing that everything was as promised, which they said would be forwarded to Heartland to register the trailer and start the warranty clock. We actually signed that on September 2.
The date of purchase was recorded by everyone as September 1 and that's when the warranty clock started.