hot d@m first time seeing this, what a fun project.
but don't u just hate the fact u don't have the time to work on it though ugh!!
just throwing an idea out there, u might be to far into it now to add it anyways, but how about adding some sort of hydolic lift so that once that bad boy is opened it can lift and rotate above the walker to aim forward. Something simple might work by just adding some pvc between the canon itself and is undercarrige attached to the walker. And just for clarification i don't mean anything spring loaded or actual working lift mechanism. Just remove the gun from walker add the lift and put gun back on to give it the "look"
Only reason i suggest it is cuz thinking real world a gun like that would suck if it could only shut backwards and a lumbering machine the size of a walker would take a while to turn around