Nice work, RoyM. 10/10 for inventiveness!!
we had the luxury of a 4ft wide x 6ft tall arched level, positively spacious by comparison.
For the second dig (the Chamber of Horrors) we set the tub rails to one side, leaving 2ft of width to store fresh muck out of the dig. It was either sandbagged and stockpiled for re-use, or kept in the tub and trammed out.
This division of space and labour (one digging out, one mucking out, one bagging up, one tramming & tipping) made for very good progress.
MARK