Ha, Four people in the tub would be very friendly
2 can stretch out nicely. There is a 4 person and a 4-6 person which is slightly larger and the one I'm using. Manufacturer claims 242 gallons and 2100 lbs filled.
I was lucky to get mine about 3 years ago during a Walmart sale for $320 shipped and have really used it a lot in the spring and fall, mainly in my yard. The bubble action is surprisingly good.
Setting this up in your friends back yard is a good way to get invited back to their driveway, assuming that is they are somewhere close to where you want to be.
Throwing it out as a possibility not often considered or perhaps not thought practical. This is definitely portable and doable.