the jet blast keeps the heat well away from the tail, you have nothing to worry about on that.

EDIT: i noticed you are using a bell mouth on your pipe though so i assume it's not in a bypass?? if not then you might have heat issues inside the fuselage with extended taxiing. not sure if you have that problem with your A4 but i do on mine so it's just something you might wanna keep an eye on during those first runs.