Adam - according to Essery and Morgan, the diagram 1828 had an all steel body with corrugated ends, and a 9 foot wheelbase.
10 foot wheelbase with a vertically planked body and early type corrugated ends were to diagram 1812, 1830 and 1808, with 1812 and 1830 being fitted. I haven’t found a picture yet.
And... I’ve just found my Essery. This confirms 1828 to be a wood-lined steel body, but still no photos... There are photos of 1808, 1812 and 1830, and (you’re not going to like this) whilst they have no external vertical or diagonal strapping on the sides, there are no external bolt heads. And on the curb rail, there are only the three external bolt heads to the left of the door as you look at the wagon. No external bolt heads on the right-hand curb rail (photos on pages 35, 36 and 37).
Hope that helps.