I bought my new 5'er last year from a dealer 300 miles away as the local dealers did not have the model I wanted. I negotiated everything over the phone and thru emails. I low balled slightly under what I figured would be a fair price knowing they would counter higher. I told them what I wanted to pay for the trailer including all dealer fees such as documentation, prep, transport fees etc but not including registration and tax as well as what I wanted for my trade. We went back and forth a bit but came to an agreement fairly quickly.
To start the negotiating I requested the MSRP build sheet that shows exactly what options where included. Worked out great.