We picked up our 2017 16 Deluxe this past spring.

• Have not noticed any water issues with the roof mounted vent. I do see minor water issues with the lower vent at the back of the refrigerator. When you open (or take out) the lower vent cover you will note the vent frame is very level and flat and won't really prevent water intrusion. (Hard to describe in words) I intend to add something at the lower edge of the frame to help keep water out. As with any vent a stream of water from a garden hose would easily overcome any vent but normal rainfall and gravity will keep most things dry. Just something to watch.
• We paid Scamp for the television/antenna option where they mounted the tv/antenna control/110v & 12 volt options in the rear corner by the bed/dining table. When we talked with Scamp about extra outlets for example we were able to specify, within reason, where they were to be placed. I would suggest if you want something specific for the outlets/television hookups etc. that you talk with them and plan those ahead of time. They often have suggestions that are very helpful. 
• The Maxxair fan is great! The built in rain cover, remote control, multi-speed fan works really nice.
• Yes, the second set of tail lights I think is important for safety. I asked about LED's but they had no option for those when we purchased.

We chose to add just about every option they offered as retrofitting was beyond our capability. The prices seemed very fair and they were very helpful and easy to work with. Love ours and have enjoyed many trips this summer.