I got my mits on the HB Tanker, & noting the comments on Armorama, I submit my tuppeny ha'porth to the discussion.

I haven't seen any size comparisons with the eponymously genteelly elderly Italeri Closed Cab Water Tanker, currently on re-release with D-Day Anniversary Flash on the box. 

So I've compared them & pics here. 

Dimensions in mm;
Door:
Height: HB:23.4mm IT:24.55mm 
Waistline at moulding: HB:21.7mm IT:23.08mm
Width at bottom of door: HB:23.4mm IT:24.55mm

Other DMs;
Bonnet:
Width: HB:34.74mm IT:34.94mm 
Length HB:37.61mm IT:35.03mm 
(over side of bonnet)

Wings:
Width: HB:16.26mm IT:16.09mm 
Length HB:71.35mm IT:68.38mm 

Grille:
Width: HB:40.18mm IT:39.22mm 
Length HB:16.64mm IT:16.73mm 

Tyres:
Dia: HB:26.32mm IT:25.05mm 
IT tyres are thought to be undersize anyway?

Cab:
Width at base: HB:44.38mm IT:41.88mm 
Width at waist: HB:44.02mm IT:43.24mm 
Height not measured, as not possible to get consistent measure points, see pic. 

Screens: HB screen in 2 1/2's IT in 1 'v' shape.
Height of front windscreen: HB:10.82mm IT:09.12mm
1/2 width of split-screen: HB:17.55mm IT:16.09mm

Rear Screen: HB rear screen in brass PE mesh. 
Width: HB:17.99mm IT:19.02mm 
Height: HB:07.98mm IT:07.01mm 

Conclusion: The HobbyBoss cab & Doors look 'squished' **WHEN COMPARED** to the Italeri, but worth the effort?