The crockpot is your friend...
Steve I held mine at 100F all day yesterday, then wrapped it up and put it to bed and it had a temp of 90F this morning and was in full flowered foamy bacterial goodness. It smelled like walking into a cheese shop in Paris.
Fill crockpot half full of water, set on low. Mix the salt rising starter, place in bowl, cover with plastic, insert thermmometer, set atop the crockpot.
Monitor the temp. My low setting would go over 110F in this configuration so I would switch it on every time I saw it going below 100F for about 15 minutes and that would hold it for several more hours over the hot water.
Last night I wrapped it (the bowl atop the crockpot with the hotwater bath) in 5 large bath towels and went to bed. This morning the starter was still at 90F.
I grew up in the country and salt-rising bread was part of my childhood. Now I know of no one that makes it any more. It truly is one of the most wonderful breads you'll ever put into your mouth and the extra fuss is certainly worth it. Since you are raising the dough with bacteria and not yeast fermentation, there is no yeast cannibalization of the sugars so the resulting loaves are dense and sweet with that wonderful taste/odor of a fine ripe cheese.
I have about a dozen old Kentucky recipes for it and I'll post one for you later. Right now, I have to get back to the kitchen!