I know of two on South Main, the closest (South Main RV Park) just beyond the 610 Loop on the west side of the street, making it three miles to Medical Center. The other (LakeView Resort) is a few miles further south. After our first visit, I choose not to "camp." We rather stayed at Rotary House (more than 10 times over three years of treatment).
Being further away from the facility would not have worked, as my wife's appointment schedule had us going back and forth to the different clinics from 4 AM to 10 PM any day of the week, and the times she had surgery, it was me going back and forth at those hours. We would not have had time for trips back and forth to the campground. But your treatment program may be different.
More generally, there are about 20 RV parks in the greater Houston area, or within 30-45 miles. That can be less than an hours travel to Medical Center, or it can be a lot longer, even the close ones, depending on time of day.
Tom Test
Itasca Spirit 29B