The lighter the caravan the better, Lutz is excellent at letting people know what weights are appropriate for what car, but he isn't the only regular that can give this info out. As for your choice, I would look at Lunar's and Bailey's as they are quite low in weight, but it all comes down to locality of the dealers and what deal you can strike with them, I think its reasonable to say that there are no bad manufacturers out there. You look like your going to spend quite some time in your van, on a personal level, I found that a permanent bed is great for this, but it depends on what your willing to sacrifice to get it, the nice large wash room or the tow car. Have a look at the Bailey Vendee (after checking your weights) as this has a separate bed, washroom/shower and living area. I know it's a 4 births and quite long, but if it's comfort you want you can't get much better on a single axle.
You'll have a great time, whatever you end up with.