Right back to it.
Glue the barrel wheel into the lug.
When dry glue the barrel into position. Under the barrel is a semi circle locating 'trench' which fits onto the carriage. Remember when doing this to leave a gap at the breach end so that the seats can be located onto the carriage. It is worth doing a dry run at this before gluing so that you appreciate where the seat locates. I didn't and had to sort it out after. Grrrrr.
Next up glue the periscope into place and then the last of the small wheels. This does get fiddly and is best done away from women, children and those with a nervous disposition.
Now walk away and do something else. Nearly done but there is only so much that your nerves can take.