I have stopped at this site several times now on my journeys north to south and vice versa. It's in a great location, only 10 minutes from the M74 and is a large, very well kept site that can usually accomodate you anytime, even with only 5 minutes notice!
It's in the grounds of an historic castle and has great walks around the site and through the surrounding woodland. It has a playpark for the kids and a pub/restaurant in the main area along with a small site shop. The pitches are well spaced and mostly hard standing and very easy to access.
I tend to use this site as a stop over on my way elsewhere but it wouldn't be a bad spot at all for a longer stop if you wanted to explore the Grenta Green/Borders area. It's great value for money.