Swapping a dinette for a couch is a pretty simple thing to do. Literally unbolts, sofa bolted in it's place. The space is the same size by design. It's actually easier than doing the inverse where the dinette is more open you can see where some attachment holes were etc. I would have no issue having the dealer do it. If you've ever seen the way they are slapped together at the factory you might actually appreciate a dealer taking a little more time. That said, if a particular dealer has had issues in the past, then wait the 8 weeks and get it made that way. What's 8 weeks in the off season if that's the way you want it?