Welcome to the forum!!
Sure sounds like there should be a "closeout" piece of something there. My Coleman had flaps with Velcro that would fold over to hide these gaps. Can't imagine Jayco wouldn't do the same. Hopefully someone here will have an answer for you shortly. Hang in there!
2013 Jayco Eagle 328 RLTS
2012 Ford F250 6.2L 4x4 CCSB W/Air Lift air bags
2002 Coleman Bayside Elite (traded)
Me, Momma and Charles (RIP buddy)
And introducing Sofie!! ;)