If you join the RAF then as a Technician trade then I think you will be tied up for at least a year doing your Military training and also equipment specific training. During this time you wont get the time to be doing any extra curricular training courses. At least thats what it was like in Army training for technicians.
Then you will be posted to wherever THEY want you to go with no guarantee that you'll be anywhere near a training college - let alone them giving you time off to do a course.
Also, certainly for Army trades, there was a minimum signing on period (6 years for Techs) during which time you weren't allowed to PVR (buy yourself out). Again I dont know what its like in the RAF but I would presume its the same.
If you have no real interest in serving in the forces, then I advise you to seriously consider looking at something else. The complete change in lifestyle is something that you really have to want to do. Looking at it purely as a vehicle to get a trade is very risky unless you're totally committed.
Also, everyone will think you're a gay boy.