Above on the MDF base you can see I have marked out the centre of the base, this will be where the gun fits with an entrance to the rear.
To build the pit, I start by cutting a piece of mounting board to the same length as the circumference of the circle, less a bit for the entrance, then I score lines across the board and bend the card along each one until it forms a circle.
The above strip of cardboard is about 10mm high, you will need to vary that depending on the scale in which you're building and the thickness of the model base you're using. My PaK38s are on 2mm MDF bases here.
Using super glue, start gluing the cardboard to the base, leaving about 1-1.5mm around the circle that marks the base size of the gun. I start by gluing from one side of the "entrance", working my way around as the glue sets. Super glue sets faster, hence the use here.
Once the entire length of cardboard is glued, I add a couple of angled scrap pieces to define the entrance.
The guns fit snugly: make sure of your fit at each step. The gun bases above are 60mm diameter and a gun-pit base of 75mm as I did not want the footprint to become too large.
With the sizes set, the cardboard surround is reinforced with a bead of wood glue all around the *outside* of the base. Only the outside, leave the inside clean.
|Pic to show height.
I built a few pits of vary sizes to hold 40mm, 60mm and 90mm bases (will hold PaK36s, PaK38s and 8.8cm Flak gun teams).
From here I cut scraps of high-density polystyrene (you could use foamcard, etc.) and build a rough bank up to the cardboard. I then cover that in acrylic silicon/caulk to create a smooth bank. You could use wall filler or similar here too, but it is best to use scrap polystyrene or similar to build up the bank and then filler of some sort to cover it. Just using filler to fill the entire thing will take ages to dry and may case things to warp.
When dry, I cover in wood glue and apply a few rocks (small stones) to look like desert pits/sangars, before applying fine sand to cover the rest. Make sure to remove any rocks too high up on the bank as they will interfere with the gun model and make storage more difficult. For Europe you might not want many rocks, or even any. You could add logs, sandbags, etc. instead.
When dry, I applied an overall coat of VMC Green Brown (not Vallejo, a colour I had mixed to match), but any paint colour you use will do.
After that I painted the sand, dry-brushing a 1:1 mix of Green Brown and Iraqi Sand (again, mixed colours, not Vallejo) before a final highlight of Iraqi Sand (now actual Vallejo as it covers far better). The rocks were picked-out with VMC 988 Khaki, then VMC 884 Stone Grey and finally dry brushed with VMC 918 Ivory for a sun-bleached look and to provide contrast. You can vary the colours to suit of course.
The end result looks something like this: