adam, I hope you do well.
I have never been a fan of mounting machines out the back, the reason being is you loose the space on either side of the unit or at least the usefulness of it on either side when its going out the back. if you mount it out the side door, it can be mounted right to the back seats, put a tall skinny reel mounted out the back all the way to one side, in this setup there is actually a little bit of room left.
as to dodge vans. I think they are a pretty darn good van, dodge didn't really change very much over the years so the parts were proven and simple albeit dated and ugly looking. I have a 2004 ford e350 that is a great van, but if I was going to buy something older I think dodge would be my first choice.