Well, Mexwanderer, with his extensive knowledge and experience with alternators would be the "go-to" guy on implementing an external regulator for your system. He has posted about various off-the-shelf devices.
My concern would be about heat effecting the chassis alternator and possible failure. I had an alternator fail suddenly a couple of months ago and even though only 6 miles from home, it involved a lot of logistics and falderal to get the vehicle back home. Replacement was another circus and I never did get the equivalent alternator as a replacement.
That ordeal sensitized me to how I want to treat my alternator in the future. There's no way I'd put an excessive draw on it.
