Howdy,Smokeskogee.
Welcome,and how's things in NOLA?
There is nothing wrong with moppin',other than it takes about 25 mins to get back up to temp.
If you start too early,you risk washing off your rub.
There is a lot of internal moisture in a butt,usually a little too much fat cap,and often injected with 10% + solution.
I often have butts on racks above butts,which bastes as it goes.
I just recommend trying it without moppin' and then change what doesn't suit you.
If you are trying to affect flavor,it may help some.
There are other ways to approach the flavor issue.