Hey Yeti, i think this is looking good so far. I love the groundwork and your base appears to be just the right size. I reckon you can turn this into something pretty good. In the first photo the dark coloured grass looks like it has been burnt, which would be an effective idea for a diorama. I might have to try that one day. The grass is not always green!
In reference to Kykeons comment about the gun trailing arms....it be easy to 'dig' up your base and sink them a little. You could then fill in around the 'spades'. Maybe build it up slightly at the rear of the spades to simulate how the guns recoil jolts the gun backwards.
One last constuctive comment. The gun could use some subtle dry brushing to 'pop' out the detail. It is amazing how effective drydrushing is. I still remember the first time i successfully drybrushed a model....i was so proud of myself. I couldn't believe the difference. Don't go to heavy though...
Anyway, i do not profess to be an expert on dioramas, i have not done many and those that i have done are not worth showing here......lol. I have so much to learn myself, but i have noticed through peoples comments on here and studying their work that it is the little details that turn 'just another diorama' into a work of art!.....the difference between hearing someone say 'that's nice and 'WOW, thats awesome!....
Keep up the good work. Hopefully i can start to post some pics too. I just just have to steal my mates digital camera first........
Happy modelling..
Hop