I think what is meant by a mobile Mikveh is a kit that convert the standard bath tub into a Mikveh. For example, you are on vacation and there is no Mikveh available. You use the kit to convert your hotel/motel’s bath tub into a Mikveh and when it’s no longer needed you convert it back to a regular bath tub.
As far as having a Mikveh in the backyard there are privacy issues as people can see over the fence or via drones unless the users are wearing bathing suits.