I may have beat you to it Phil, this was in 2010/11, no way to get bigger on ein there, a real bargain too, brand new off their own ebay site £150 delivered
I see someone was bright enough to use proper truck barn door catches on the new van Phil, I always fit them to the vans Hab doors as the MoHo oen are really not fit for purpose.
I've seen them weld on tanks and such on YouTube Phil, what they mostly seem to do it pipe exhaust fumes in to it for a while it must do something to the fuel fumes, I never did kemystery of fizzics.
Video is interesting roughly shows what you get and how it fits
https://video.aliexpress-media.com/play/u/ae_sg_item/17380645214/p/1/e/6/t/10301/301904137321.mp4?from=chrome&definition=h265
You should have an idea of what you want it to have and how many people/dogs/etc. will be travelling/sleeping in it. You should also have an idea of your budget. Will you use sites or a wild camp?