Heather,
I don't know anything about MS, but I am currently doing in-center dialysis 3 times a week. I am planning to buy a MH and have been researching dialysis options. Here is what I know.
If you (or whoever you might be inquiring for) are currently doing in-center hemo-dialysis, you can continue to do so as you travel, but it takes a great deal of planning and you must stick to a strict schedule. This is less of a problem if you are staying in one location, but if you are always travelling it can be difficult. A mechanical breakdown could completely ruin your schedule. Most dialysis centers are heavily booked and can't just squeeze you in. The advantage to this method is you don't have to haul around equipment and supplies.
Another option is Peritoneal Dialysis. I have no personal experience with it, but it does allow for a great deal of mobility. The disadvantages are having to care for a catheter and having to stock a lot of dialysate.
The third option is home-hemodialysis. Check out www.nxstage.com. They make a home-hemo machine that is 15"x15"x18" and weighs 75 pounds. This could easily be transported in a MH. Medicare will pay for the machine and your supplies. The biggest problem with this method is water.
There is an optional device that will make dialysate from a chemical packet and water that you provide. It is 19"x20"x26" and takes 7 hours to make a batch of dialysate good for 3 treatments. You must have access to water that meets EPA standards though. Every municipal water system has to meet the EPA standards, so if you are in a city this is not a problem. However, some RV parks are on well water and all bets are off.
Instead of making your own dialysate, you can use pre-packaged dialysate that comes in bags just like saline. The problem is a months supply is a palette load that weighs about 1000 pounds. If you are only going on short trips this isn't as big a problem.
Those are the main issues I can think of right now. Obviously you should talk to your doctor, your dialysis center, and do lots of research online and otherwise. There is plenty of information available. I haven't found it in one place though. The main thing is this is do-able. It just takes a lot of pre-planning and some determination. Good luck.
Mark