He was great. I just did a track for him two weeks ago, where they changed the key on a song he wrote; it didn't have his vocal on it, and I doubt he got one on it before he passed.
Back in the 80's, when I was out with Tammy Wynette, we did a bunch of shows with him. She called over the walkie one night to our bus, the radio crackled, "Mikey?" I answered, "Yeah, Tam, whatcha need?" "Would you get my guitar from under the bus and bring it over here to Hag's bus? We're gonna sit and write a while." I said, "Sure, be right there."
I walked onto his bus, back to the stateroom, we did our introductions and howdy's, and I saw a Lazy Susan on the table. On it was a selection of ANY "substance" known to man. I looked at it wide eyed, and Merle said to take anything I wanted. I just said, "I'm good... but thanks..."
We didn't leave the venue for quite a while...