Hit the local salvage yard and find a conversion van. Most have quick release captains chairs in the rear that swivel... and the bases are bolt in.
We snagged a pair of swivel bases for next to nothing... seats were junk. Found a seat that folded flat and modified the swivel base. Here is ours...
IMG_20181011_181448383 by
acidburn02zts, on Flickr
IMG_20181011_175307725_HDR by
acidburn02zts, on Flickr
IMG_20181011_175219558 by
acidburn02zts, on Flickr
It slides a bit further forward then pictured which gives plenty of room to walk behind it. When we are stopped for a few days, it takes 10 seconds to pull the release lever and the seat pops off the base. When folded up, it fits nicely in front of the passenger side dash leaving the whole entrance to the bus open.
Here is the locking base...
IMG_20180729_174344523 by
acidburn02zts, on Flickr