Hi Jules, not sure if this is helpful, and it certainly isn't advice, just some things to consider.
Although your husband says he wants to totally quit smoking, is he ready to do so right now? I have said for many years that I want to quit smoking, however....I've been waiting for the time when my mind tells me "OK...enough of this, you need to stop now". Unfortunately, I actually enjoy smoking, so the times are very few and far inbetween for my mind to be strong enough to just quit and therefore, have been rather unsuccessful in my smoking cessation. That fact is currently true for me. I'm a pack a day Marlboro Lights smoker but since actually dedicating myself to vaping, have only smoked 2 packs of cigarettes in the last 20+ days. Nonetheless, I have not completely given up smoking! Until my mind is strong enough to give me the willpower to completely stop analogs, I look at vaping as the alternative.
What is missing from his vaping experience that makes him miss his cigarettes? Smoking and vaping are definitely not the same (as you well know). I still find myself wanting cigarettes. It might be helpful for your husband to figure out what it is that is not being satisfied by his vaping.
Sub-categories to the above question: Has he found a model/type of e-cig that satisfies his vaping experience, or does he need a different type/model? Has he found a flavor(s) that satisfies his vaping experience? Does he feel overwhelmed and under educated about vaping and what exactly he is doing?
I've had the fortune of taking the past 3+ weeks off from work, so I've been able to spend massive amounts of time understanding vaping and experimenting with it to see what I need to gain enough satisfaction from vaping to make it a substitute for smoking. I also introduced my girlfriend to the e-cig at the exact same time. However, she has not truly applied herself to understanding what it is yet and therefore, has not dove head-first into this as I have. I plan on continuing with my vaping as my primary smoking experience, knowing full well that I will have an analog or two every now and then. In the meantime, I will continue to make e-cigs available to my girlfriend, continue to try to educate her on it, and continue to test flavors to find one that really grabs her, which might allow the e-cig to become her choice for smoking. Right now, it's just too strange and too complicated for her to dive head first into. Your husband may feel similarly.
Hope this helps and I wish you and your husband the best!