Hanomag 251 Half-tracks: Mortar carrier variant
Both these vehicles are based on the B version of the vehicle, which saves a lot of work. My excuse for this is that mortar carriers probably sustained fewer losses than front line half-tracks, since they lurked at the back of battles.

Here you see the two mortar carrier vehicles I have made, before painting. After painting, the alterations to the basic kit won't show up so well. In the foreground is the base of the crew cartridge, with scratch-built 81mmm mortar. On to this will be glued a couple of crewmen. If the mortar dismounts, or the vehicle gets blown up, the cartridge will be removed. In the vehicle on the left, the cartridge is in place, with an SHQ white metal mortar. The mortar base plate on the vehicle floor is a half-cylinder shape. The front legs of the mortar rested on the sloping sides of the vehicle, so the cartridge had to reflect this. The square notch in the front of the cartridge fits around the central raised portion of the floor, between the front seats. The scratch-built mortar is made from plastic rod, sprue, plastic card, and old paint tube (metal foil), based on the SHQ model, with a few extra details from plans.
Note the radio aerials on the front right of the vehicles, for receiving word from the forward observers. These were very fiddly things to make, as the bottom bit is a complicated shape, and I used many tiny pieces of plastic. The aerials themselves are artificial pine needles from a Christmas tree, which were super-glued into holes burned with a hot pin in the ends of the stalks.
The vehicle on the right has lost the mudguards over the front wheels. This was very common. Sometimes they were removed deliberately. The headlamps have been added above the right front visor and below the left side visor, and have slits burned and trimmed into them with a hot pin and a scalpel. The front wheels have been cut off the axle, trimmed at a slant, and glued to appear turned to one side. The kit had a recess in each side of the nose of the vehicle, into which fitted the front parts of the mudguards. These recesses have been filled with Milliput putty.
Looking inside the left vehicle, you might notice that there is no steering wheel. That will be added after I have painted the inside floor of the model, and then glued it in place. If you glue the steering wheel in at this stage, you can't get the floor in and out.

A top view of the same two half-tracks, both with cartridges in place. Note that the mortars fire forwards, and that the muzzles are just above the level of the sides of the vehicles.
The base plate for the mortar when it dismounts was not stored always in the same place, and some depictions show it on the outside of the vehicle, which is where I have put mine. I wanted it there because it looks nice. On the top vehicle, it is on the left rear, and on the bottom one, you can just see its top edge on the right rear door.
Neither vehicle has a front MG. On one, I have placed a rifle in its place. These vehicles were equipped with rear AA MGs, but these have been left off until the final stages of painting.
From this angle, you can see the fit of the cartridge quite well, with the angled pieces of the base resting on the side walls just behind the front seats.
The rear right benches have been removed, and replaced with a low shelf on which rest ammunition boxes, made from a sandwich of plastic card, with a design scored on the flat sides with stylus. By pressing the parts of the sandwich together while the plastic is still half-dissolved by glue, the effect of raised lines of detail on the edges is achieved. I have glued the boxes in a staggered formation, because after going to all that trouble, I want it to show that they are all separately made. I glued one on the seat, overhanging. You can see that I have had to cut a little triangular piece out of the cartridge base so that I can get it in and out easily. You may wish to avoid this folly.
The personal stowage on the left side of the bottom vehicle is made from sprue and plastic card, or else is cut off from unwanted figures. Get an infantryman, cut off his boots, helmet, pack, entrenching tool, gas mask canister etc., and glue them onto a vehicle, for some detailed clutter. Make sure to carve the boots flattish, and add a suggestion of a hole at their top. You'll want super-glue and/or universal adhesive to glue on polythene pieces to the polystyrene kits.

Here we see the finished models on the wargaming table. The one on the left has no front mudguards, and I have splattered extra mud on its nose accordingly. You might just be able to make out the black oily hand print painted on the left side of the nose. You can see more black oil painted oozing from the little hatch on the nose of the right-hand half-track. You can see a jerry-can painted black with a white cross. This was the standard marking for a jerry-can which contained water. Both British and Germans used this marking. The camouflage pattern, sand ("dunkelgelb" - literally "dark yellow") with brown crosses, is an authentic one. Barrels by Hovels, AT emplacement by Faust, crewmen by SHQ and Esci.