Would it be permitted according to sefaradim to cover with foil paper before shabbat the inner part of the crock pot, or will we say that it would be hatmana and assour,and it is just the top that is covered and bent a little on the sides so that the foil paper should hold, please let me know asap, thank you.
I understand that the purpose of doing this is to “distance” the pot from the heating element, so that the crockpot will not have the status of hatmanah be-miktzas, which is forbidden according to the Shulchan Aruch 253:1.
I do not think that a layer of silver foil will help for this purpose, because this is not considered a “separation” of the pot from contact with the heating element.
However, note that there are some who write that since the pot does not lie flush against the heating apparatus, this is not considered hatmanah, and is permitted on Shabbos even according to the Shulchan Aruch (see Shaar HaTziyun 257:43; this is the opinion of Rav Chayim Pinchas Scheinberg, cited in Otzaros HaShabbos p. 519).
The best way to permit the use of a crockpot is to elevate the pot by placing a stone or metal item inside the external apparatus. By doing so, the pot protrude above the heating elements, and will usually no longer touch the sides, thereby permitting its use even according to the Shulchan Aruch.
Note also that even according to the Rema, there are poskim who did not permit the regular use of crockpots on Shabbos, and the method above ensures that it is permitted to use. However, some (in addition to the lenient opinion above) maintain that according to the Rema there is no problem because the top of the pot is not covered (based on the Shulchan Aruch Harav 253), and those (Ashkenazim) who are lenient have whom to rely on.