Ideally, if you positioned yourself well behind your Bullet and looked towards your TV, you should be able to see the whole mirror. Obviously, the farther it sticks out, the better. It depends on how much your stock van mirrors extend out from the van. I doubt if they would extend far enough out to give you a good and safe view of vehicles approaching from both the driver's and passenger's side.
You may get an extended view by using a stick-on convex mirror but to be on the safe side, I would do whatever is necessary to make sure that you have a good view of the traffic in both lanes behind you. You are essentially talking about your safety here and I wouldn't scrimp on merely buying a couple of stick-ons and saying now I am good to go.
Having a good view is necessary not only when you are in traffic, but also when you are backing up into a campsite.
2008 Cougar 5th Wheel 27RKS
2005 2500 GMC Duramax