I feel you really need to decide your caravanning lifestyle before looking at particular models of BBQ. If you like to go to one particular site and stay then a larger, more efficient BBQ makes sense. It can be stored in the main body of the van for travelling and erected once on site. If however, you like to do a lot of touring then a BBQ that is occupying floor space is maybe not such a good idea. Here a smaller, possibly less efficient model will supply all you wish and be able to be stored out of the way until required. BBQ's are only one part of he fairly extensive kit that we all seem to carry these days and need to be considered as part of the total package.
My wife and I adopt the latter category and therefore use the small box shaped gas BBQ's that were introduced by Calor some years ago. The lava rock base is good enough for cooking anything especially in the sun of the Med, and yes, it maybe isn't up to Weber standards but that is acceptable to us. With a bottle of chilled white wine who cares. It also hides away in an under seat locker when not required. We also use an electric grill as an alternative, this grills extremely well but of course doesn't provide the 'smoky' flavour.
The other factor to consider is how many, and the ages of the people in your party. If there are just 2 elderly adults like us then a smaller model is fine. If you have teenage sons, and we have been through that, then a much larger model is definitely required.