I once rented a cargo van to buy a mattress and bed frame from IKEA. It turned out that I didn’t need the van at all and could have packed everything into the 4-door sedan I had at the time. Part of it was because the mattress was rolled up in a compact manner. I seem to recall that the van could easily fit in one spot.
It does seem that there are box trucks based on the Ram pickup chassis, but I don’t think I’ve seen those in person. Most box trucks I see here in Canada are either based on a van chassis (usually Ford Econoline or Chevrolet Express/GMC Savana, but sometimes European-style vans like the Sprinter), the Ford F-650/750, or an actual truck chassis, like an Isuzu cabover or something from a company like Kenworth or International.