I believe the Federal Government should house all long term prisoners. Lifer sentences, Death Sentences, and those serving 20-30+ years. Relieve the states of the heavy financial burden. The Feds could even become an "outsource" for states.
The feds could build regional prisons, putting to good use decommissioned military bases. Nothing too fancy, no air conditioning, no television, radio, etc, receive the bare minimum to survive, locked up 24/7/365, single cells, just hard time. Prison is supposed to be punitive, so make it so. "Good behavior" gets an hour of exercise a couple times per week, alone.
Single cells, hard time, no socializing. No choices. OK, one choice. Euthanasia. Perhaps even encouraged.
Locations could and should be in geographically uncomfortable and isolated locations. Guards and security could be recruited from existing personnel, and/or a new "service" similar to the armed forces, or as a branch of the armed forces. "Prison" employees would enlist and serve their terms on the prison bases in true "military" custom. Tours of duty could be "voluntary" if existing armed forces are used.
Unfortunately, there are probably many millions of prisoners serving long sentences. Current systems could not and would not adapt well, but they could start from scratch with "new" convicted felons and within a few decades those currently incarcerated would eventually matriculate out of the system.
Of course, there is no chance of this sort of thing ever happening.