I constructed the bogies using sheet and 12mm strip brass, I marked out the axle positions on the strip and drilled them ready to accept the brass top hat bearings which were then soldered in and the whole  soldered up the wheel sets inserted and then  some 1mm brass square tube across to add rigidity. These have been to a plywood base by bolting through with M6 brass bolts and nuts . the fuel tanks were made up with card , unfortunately no photos of this stage but photos of the finished model hand painted using Cornish Milk mineral paint, I've used this on previous models and found it really stiffens the card and dries without brush marks.