Towed artillery vs. SP Artillery's survivability
 

A HERO report (a bit old, so I dont know reliable nowadays) that covers the subject of artillery casualties in WW2 (US part mostly), Korean War and 1973 Arab-Israeli war. The interesting observation one can see from the article is that SP artillery is actually more vulnerable to towed artillery, although it offers better crew survivability.

link: http://www.dupuyinstitute.org/pdf/055.pdf

Re: Towed artillery vs. SP Artillery's survivability
 

It's really a matter of how good your oppositions counter-battery abilities are and how often you displace. I think towed artillery knows they're vulnerable so they do so often, SP artillery is often (lightly) armored and this gives a false sense of security.

Re: Towed artillery vs. SP Artillery's survivability
 

I would say this just shows SP Arty was not taking advantage of its ability to relocate quickly often enough.
If the other side has air superiority it is probably more vulnerable as it will be easier to spot.