First, welcome to the forum! I'm sorry it's under these circumstances.
Some observations; as has been mentioned that trailer has been sitting a long time on that lot. RV manufacturing is not like on autos....sort of hit and miss. The dealer should have inspected that trailer right off for anything like a roof leak etc. If they didn't and let it sit out there for a couple of years this should be on them. Of course, whether them or Keystone or ? sitting at the dealer for repair/warranty work is a real pain.
You need to find the source of that water penetration pronto....keep it covered until you do if you have wet weather. You may be able to do that by inspecting obvious places above on the roof seams, penetrations etc. Check around clearance lights as well. Yes, it's under warranty....but it belongs to you and is your investment - Keystone nor the dealer care about it anywhere near like you do.
A good dealer inspection either when they received it or prior to your possession, or your own inspection, could have found this but that is water under the bridge at this point yet again that just says they are responsible for this IMO.
Pre possession problems are usually taken care of "right here, right now" to appease a new owner so they can get their money. Once sold and the new owner takes it away it becomes a cat and mouse game - sometimes push/shove. To that end you want to go celebrate in May.
You need to be front and center with that dealer one on one with the GM/owner. Insist that they schedule you for repairs right away....not at the end of the list. They may balk but remind them, constantly, that they caused this and did not check it nor disclose it to you - push (be insistent) if required. IMO the dealership should just take it in and fix it since they let this happen but I'm sure they will want Keystone to "pay for warranty" which then requires documentation from them, assessment from Keystone and then approval - it is time consuming. Don't let them just take it in and sit on it waiting for it to hatch an egg. If they insist they want Keystone to pay for it (I would push they do it with or without approval) then let them have it long enough to document the damage/cause then take it back. Take it on your trip - HAVE FUN with the trailer. I sounds like there is nothing catastrophic or destroyed with the softness so just be careful in those areas. By the time you get back they should be ready to take it in and fix it. Make them, and the situation, work to your needs as best you can. Good luck and hope it works out like you want in an expeditious manner.