@jules22 - In short it's absolutely not a simple model to scratch model, without accurate plan prints (to scale) to work from, and modeling a van with these complex compound curves is definitely a major project.
Not something I would take on, way beyond my modeling ability.
Without knowing what brand/model that van is, we don't really have a starting point for a pre-made free/paid model mesh. We're also talking about finding a finished model mesh to start with, as well as full on left/right side, back and front views, shot perfectly in tangent to pull the logos and advertising art from. If that's not happening, then re-creating them from scratch will be a hit and miss affair depending on the person art talent in GIMP or Photoshop. May have to dish out some cash for fonts as well, if a close enough match can't be found on the internet.
EDIT: I found some other Mr Whippy pics, and determined that the van is a Morris Minor, but no idea what model it is. The only MM van mesh I could find is on 3dmodels.org, is way over detailed for a scenery asset, for Trainz, and costs 95 USD.
There is one van on Sketchfab that is a close match, but is textured in a old, beat-up rusty exterior. It's 15 bucks.
https://sketchfab.com/3d-models/ice...-cream-truck-6f58a8a3d50147b29bb3f058e02b713d
Again, the van would need to be retextured, and would need the straight on elevation shots to be able to make the texture map.
There is a possibility, if you don't care about the van brand, > One of the many Berliet or Fourgon French vans on the DLS (same era, similar design) could be reskinned.
Rico