You have to remember that even if your bar is mobile, cask-conditioned beer isn't really mobile, at least not without a day or two to settle. Obviously it depends on how sticky your yeast is, alternatives are to serve brite (which rather misses the point but is useful at parties) or to fill jugs in the basement and bring them up to the party for people to help themselves, which was the old way of doing things retained by the likes of
the Star Inn in Bath, particularly for Bass. I have got away with moving casks short distances at festivals, but you don't want to do it unless you really have to as one jolt means the cask is out of action for the rest of the day. Really you need to move steel firkins with two people to keep the movement smooth, I guess you could do it with one if it was just a pin.
Another consideration for those wanting to mix with kegs, is that British cask beer should officially be stored/served at 12-14°C (54-57°F), although since I'm a slow drinker I like to serve it very slightly cooler than that (10-11°C, 50-52°F) so that it warms up through the sweet spot whilst I'm drinking it. But serving at fridge temperature kills it.