Honestly, if you're not showing him in halter, don't even put him through it. You have to religiously sweat a neck to get any results, and to maintain results, you must keep sweating them every day.
With his thick neck, he'd need the max sweat time, plus a rigorous work out on a line to get him hot enough to his neck will sweat, and will continue sweating for two hours(max. Time). During these hours, he needs to stand, tied, in a draft-free area (again, keeping him HOT and sweating, and from getting him chilled).
I know some hardcore halter people sweat for up to three and a half hours.
Then you have to worry about skin and hair care. You're going to need to rinse him off with water, completely after you sweat him - or he's going to get itchy and irritated. Then you need a leave-in conditioner to keep the hair and skin from getting dry and brittle.
Sweating has great results, but with great results comes great effort and a lot of hard work that just isn't worth it to you or your horse unless you're showing halter every weekend.
I've got a lovely bunch of Neuticals,
There they are all standing in a row
Big ones, small ones, some as big as your head