Its all in the details. The Thor products usually tend to be mediocre quality, but it seems like all RV's are that way lately. What was mentioned above about tank sizes is one of the most important things and something I cannot seem to get right. To me, 20 gallons is way too small but I have not looked as specs for B models. Be aware, Class B models are more and more going to cassette type toilets. Its a matter of preference, so I mention it to make you aware of it.
It appears that Thor builds straight Class B models on the RAM Promaster chassis and the MB Sprinter chassis. Personally, I don't like the Promaster due to the fact it is front drive. It does allow a lower frame and floor, but it also make service much more difficult. Thor is not using the Transit chassis on the class B line.
It appears that Winnebago is doing the same thing, using the cheaper Promaster chassis for the lower priced B's and the Sprinter for the top of the line models. No Transits. I will say however, look hard at the WBO products as they are better quality than the Thor (generalized statement). One thing I did learn is that Winnebago actually has parts catalogs, wiring diagrams, plumbing drawings, all specific to the year/model/submodel/serial number group of motorized RV. Readily accessible and can be saved for offline use years from now. No other manufacturer has this, and its worth it when time comes to repair or modify an RV.
To me, the best van is the Transit (or the Sprinter if you have money, lots of it). This article linked below does not consider the
Pleasure Way models or the
Leisure Travel Vans, both are Canadian manufactured Class B or B+ RV's that are very good quality and popular, but pricey.
The following is an other wise useless article on Transit based class B models. It mentions the Coachman Beyond, the others it lists are all custom built off road types.........
Link to the not too informative article.
Coachman Beyond corporate website
Charles