Would it make any sense for two people to go in on one press?
Looking at the Dillon 550B, it looks like it could be mounted to a piece of plywood as a platform and that platform could be c-clamped to a workbench while in use. This would facilitate moving it when necessary.
When I got my 550 that was my exact plan. I bolted it to a chunk of 2x12 and used a deep C-clamp to hold it to my workbench. It works well. On some cartridges like new .500 S&W it moves a bit, so I can't thrash on it, but it's never come loose. If I'd used *two* clamps, it wouldn't move at all. I'd go for 2x12 and not plywood, unless you want to use some really thick plywood. dimensional lumber allows for much longer bolts to hold it down, and won't twist/bend as much.