President Trump Says He Will Be Arrested Tuesday, Calls for Protests, page-33

Good question.
First SS security is not mandatory for a former president, they can decline protection.

Now I am sure Trump would be happy to subject SS security to sharing his cell but I would suggest they would not be required, lest not while he is in a cell

Reality is that Trump will use delay tactics avoid going to trial then when eventually convicted he will appeal all the way to the supreme court while dragging it out so he will be dead before he runs out of appeal options

As disappointed as many will be Trump is likely to send little if any time in jail