This was a tear-jerker article, but one-sided. We need to realize that these guys move around a lot to see the country and spend on gas, expensive food on the road (ribs for $21 ?).
Regarding the single woman, she clearly wants to travel around and the article says "She could hit the road, but she will have to keep working". Her income of $1390/month is enough for her not to work if she stays put in one place and rents a room or small studio apartment for $390 or $490/month. She'll still have $900-$1000 for very cheap home cooked meal and other expenses. RVing is expensive with gas, renting on RV lots, expensive fast food, and maintenance for the RV. Traveling expenses pile up.
The couple with the guy having a $2,700 pensions from the military + disability .. could also stay put and rent a cheap apartment and survive. He lost the house because his mortgage was $2,150/month. But $2,700 military pension is plenty to survive on and rent a cheap apartment. Again, they just want to travel, so travel expenses cost money and they have to work as janitors.
The last couple didn't have stats on their income, but it says 'he works at RV campsites ..and dabbles in photography, fly fishing, and gold panning' and she says 'we have a warm bed, food, etc." So, the guy has work income but no savings. It does not say if they have SS or pensions. I think the third couple is the most hard up.
Lastly, this is an LA Times article .. so these guys are mostly in California. CA is an expensive state compared to many southern states. But I have a retired friend who survives on $900/month SS in CA for rent and food. For travel/entertainment, she has to do some work.