It sounds like you are going to use it for only two weeks a year.
Have you considered renting a MH? Will they rent to you if you have a dog?
Can you rent a MH one way?
Rent on west coast and drive it east, visit family and rent again for the westward trip.
I don't know how much it costs to rent like that, but if you divide your annual MH costs by 2 weeks of use it won't be cheap either.
Rent a big rig when you have 4 people. Rent a small one when it's just the two of you. No dealing with storage or trying to start a rig that has been sitting idle for 8 months. This would also give you the option from starting from a new place every year.