Northern Lite is a very good choice. Other than the obvious structural damage, water damage is the only thing that I can think of to look for; move the mattress and check under and around it for mold; check inside all the closets and cupboards; check the roof for damage or holes etc.
Nothing should ever be bolted or screwed to the roof other than the ceiling and fridge vents, the factory installed TV antenna, or air conditioner. If it has an aftermarket air conditioner, be sure that the installer used the N-L spacer between the A/C unit and the roof. That spacer is needed to properly support the A/C unit. If it has solar panels or any other items on the roof, they should have their mounting brackets glued/taped (3M VHB tape) to the roof. The roof is strong enough to walk on but not thick enough for bolts/screws.
Take a look at the N-L Owners forum
Click Me. Join our group and ask questions. The forum members will assist you.
LeRoy
EDIT:
I forgot one thing. If your truck is a 2011 or newer model, you will probably have to put a 2 inch spacer under the camper so that you have clearance over the cab. This will probably be true for most older campers.