So, the short version is: I've been using a saturated epsom salt solution (enough salt so that there is a bit salt remaining) and use a sponge to apply this to my body, twice a day, in the morning after showering and in the evening a couple of hours before I go to bed. This has stabilized me in a time where my RLS was ultra bad and helped me long term to reduce my medication a bit, from 20mg oxycodone to 15mg. But more importantly, whenever I make an attempt to get rid of this inconvenience I experience very bad nights. So this has helped me for the last half year or so, it's not a short-term thing. And I would encourage you to try this treatment if you have RLS despite good iron status. (I had the iron IV and it didn't help at all.)
Long version: I know that I have an oxalate issue, as eating high oxalate food reliably worsens my RLS significant. (Another long story, but let's just say it was a very controlled n=1 experiment that I repeated several times.) On the other hand, I've been on reduced oxalates for 3 years and strict low oxalate diet (<50mg) for the last half year and, while I've seen slight improvements with my fatigue, my RLS hasn't changed. So apparently it's not oxalates alone, or I produce a ton of oxalates endogenously.
Still, when I went on the LOD half a year ago my RLS went completely out of control, within a few days of reducing my oxalates to 50mg. I used to take 20mg oxycodone, I had to go up to 30mg plus l-dopa and still had fairly constant RLS breakthroughs. Which would in the low oxalate community be interpreted as a sign of "dumping", the body eliminating oxalates, which is fairly common after cutting out oxalates. One of the remedies is using epsom salts, because both the magnesium (which eliminates oxalates, among other things) and the sulfates (used for detox like glutathione) are often deficient in people with oxalate issues. Now at least for magnesium there is a hard limit of oral supplementation, because, you know, diarrhea. (And I test this limit daily and still my bloodwork shows a magnesium deficiency.) And the idea is that by putting on about 20 to 30 grams of magnesium sulfate on your skin per day, a small portion of it will go through the skin, enough to make a difference.
Now the effect was impressive. Within 3 days I was back to 20mg and no l-dopa, and slept like a baby. The effect wore off a bit, but I am (on most days) able to skip my morning dose of 5mg oxycodone. And as I mentioned, without the epsom salts my RLS symptoms become a lot worse, which I try perhaps once a month.
The classic way to apply epsom salts it is baths, but the recommendation from Susan Owens (an oxalate researcher) is to use a sponge because it's much easier and cheaper than taking baths, especially if you do it often (I think the recommendation is half a pound for a full bath). Plus the stuff is on your skin the whole day. (The minus side is that you shed magnesium sulfate all over the flat. But after a while you figure out how to use just enough so that this is minimal. And it washes off clothes and can be picked up with a vacuum without any issues.) In fact she used it to treat his father who had dementia and would jump right out of a bath.
And it's fairly cheap, after my initial experiments I bought a 10-pound container (pharma quality) for something like $30, and this will probably last for the better part of a year.
Oxalates have been discussed in other threads, but a very good introduction would be Sally Nortons "Toxic superfoods" book.