Security for whom? Presidents are not above the law; if Trump is convicted of a crime, I see no reason to give him more protection than any other inmate.
If you’re worried that Trump will spill secrets to his fellow convicts from his time as president, that would be worth considering.
The law says that ex-Presidents have a Secret Service detail to protect them. That doesn’t stop if they go to prison.
Does it? I thought that was just policy at the discretion of the executive branch. Push comes to shove, the Secret Service could just deputize the prison guards.
And both the Secret Service and prison guards are used to working together with other security services.
By law, former presidents are entitled to a pension, staff, office expenses, medical care, health insurance, and Secret Service protection.
The protection is the same: to keep the inmate safe, including from other inmates.
For some inmates who are at greater risk, that means higher degrees of security, to achieve that same standard of safety.
They have to protect him, but it does not say how.
If imprisoned, he is likely to continue to get threats that need to be investigated, especially if they seem to be coming from a fellow inmate.
It would be a mistake for the Secret Service to act as amateur prison guards. But the Secret Service probably has a higher opinion of their abilities than I do.
If a fellow prisoner was harassing Trump, and the guards were too busy to deal with it, then he might need in person protection.
Prisoners should be treating each other respectfully. Guards should enforce this to the greatest degree feasible, regardless of who is the prisoner.
Can we just freeze him in carbonite?
If you hit a slab of carbonite hard, say with a sledge hammer, would it shatter?
Asking for a friend.
What did future generations ever do to us?
Well, no one says he ever has to be unfrozen.
It would be trivially easy to accommodate the Secret Service in prison (for what would be the most boring detail of their careers). We have lots of experience imprisoning “special” convicts—governors, senators, etc. For an international example, South Korea sent an ex-president to the slammer. We could literally construct facilities for him alone.
There is zero reason Trump can’t cool his heels in prison.
Probably not: “He should be quite well protected. Provided he survived the freezing process, that is.”*
Appreciate your friend’s initiative, though. 
*My personal technobabble is that the carbonite is just a matrix supporting the formation of a stasis field.
That’s not a foregone conclusion. Although there could be challenges, and at least one person quoted in the article below agrees with you, there seem to be no truly insuperable barriers. And the agency seems to be planning for the eventuality, according to a former agent.
Gertner said the Secret Service has handed off security duties in the past, such as when former first lady Hillary Clinton was protected by State Department security as secretary of state. The Secret Service can direct and oversee protection by others, assigning a special detail to work inside the Bureau of Prisons, or potentially helping prison officials enforce a custodial sentence at home — potentially such as at Trump’s Bedminster, N.J., or Mar-a-Lago residences or elsewhere.
If Trump goes to actual jail, I suspect his health will start acting up. Not his real health mind you, just his imaginary health. Like he’ll have a sudden flare up of bone spurs kind of situation.
In fact, on further reflection, I will even predict what it will be. It will be the prison food causing him stomach issues. It’s a complaint he can make that sounds like something that is being done to him intentionally rather than him just being a wimp. The Deep State is trying to poison him, the clear front-runner for the 2028 Republican nomination.
The wrong kind of ketchup on the hamberders.
In my experience with clients at the local correctional centre (IAAL), the meals are nutritionally fine, but tend to be bland and unexciting. Green salad, meatloaf, mashed potatoes, canned peas, bread, butter, a fruit cup, and coffee, tea, and/or milk would be a typical dinner. There may be packets of condiments on the side—Trump would probably require more packets of ketchup than the average inmate gets, but they would be provided if he asked. Anyway, you can imagine all the variations on this “meat, veg, potatoes” menu, but the fact remains that pretty much all inmates will get it. There can be exceptions made for religious or health—mainly allergic—reasons. Regardless, many inmates will “jazz up” their jail-issued meals with purchases from the canteen, such as a Coke instead of milk, or some potato chips to have on the side; but the fact remains that no matter how dull and boring and bland today’s offering is, it won’t kill you or make you ill.
If Trump says that he requires something different than what everybody else gets, and which keeps them alive and healthy, and he cannot claim a religious or allergic exemption, and a physician’s exam shows that jail meals do not affect him in any adverse way, then he will get jail meals.
Sorry, Donnie. Enjoy that meatloaf. You want more ketchup?
I wonder whether he’ll try to get them to let him keep his Coke button.
“I need ketchup! What’s this ‘catsup’? I know my rights!”