I love my basement AC, after I fixed the seams problems the OP decribed.
And I would never buy an RV with noisy roof ACs.
All you need to do is seal your duct joints and you too will love your basement AC (again).
Winnebago cheeped-out on insulating and sealing the vents on the rear cap, but this is not reason to run away from the basement AC configuration so many people complain about, when all they need to do is fix their venting problems.
2004 Itasca Horizon 40AD