This is the one I am referring to and it is not flimsy by any means. Thick canvas, steel poles, super thick floor. I've not personally had it in much rain but no reason to believe it would have an issue.
I've got a Safari Henne Bow tent taking up space that I'm not using. Check them out, heavy duty canvas, no-see-um mesh, used in Africa and other places outside for months at a time.
My wife and I are a big fan of your story and follow you on Youtube. We have been researching vans and the like for our family of four + dog (2 - 6 month olds) and you've provided plenty of ideas to consider.
In hindsight with how you've outfitted, use, and money invested in the van, do you...