Since your Sunline was pre-wired for A/C, that would also mean that the roof in that area is also built strong enough to hold a rooftop unit. Installing an A/C isn't too terribly difficult, but there are still precautions to be taken. Your unit being an 85, I would also tend to think that the roof is strong enough to walk on. I would test the roof, before committing my full weight on it. The post-1995(?) units came with a rubber roof, that was not meant to be walked on. There is a procedure HERE
that explains how to properly distribute your weight, should your roof not be up to it.
As far as installing the A/C itself, I did an install on our fifth wheel. It was also pre-wired for an air conditioner. The process won't be exactly like mine, but you should be able to glean enough useful information to be a help.