I'm as familiar with Sleap as flying there yesterday will allow....
Quite true about Shawbury as Sleap is within the zone, so lots of practice to be had asking for zone transits and the like. My experience of military controllers is that they're a great bunch of folk, who go out of their way to be helpful.
However, if all your lessons are at the weekend, you won't be speaking to Shawbury very much as, like most British military establishements, they're closed by and large at weekends! A tip to any invaders - do it at a weekend if you want a quiet life!