Hey Dave,
As you can see from my signature we are another vote for the Q5!!
Situations like Kevin (Recumbant615) are rare, however I did anguish over whether I should have a slider when purchasing our first 5th wheel a year ago. But like Recumbant615, consider your storage situation and make the right choice for you.......if storage is good, I would not worry about campgrounds and "normal" driving scenarios. Now that I am no longer a "rookie" with over 25 weekends of camping around the Carolinas, I would not be concerned with the added expense of the slide........I have a very tight cul de sac to turn in near the house and I do get dawg-gone close to the 90 degree pivot!! (truck is the 2500HD CC with standard bed)
On the airbag question....YES! I added them about 2 months after our purchase and they greatly improved the ride.
Good luck with your purchase........you will love the Heartland "community"!!!
Lance