In Finland:
At least PPL (SEP) and GPL When a PPL holder wants to fly GPL validation, minimum is 10 flights / 2 hours.
Tow pilot must have total experience of 150 hrs, of which at least 100 hrs in powered aircraft. Max 30 hrs of previous can be flown in TMG's (one can calculate 50% of logged time in TMG). Remaining 50 hrs can be glider time.
Tow pilot validation requires 20 tows of which at least 5 must be flown with instructor. Tail-dragger or not is not any kind of issue for insurance companies. Clubs are just not giving their valuable towplanes to anyone.
BTW, towplanes can be experimental as well. Two of my clubs use PIK-tugplanes (PIK-15 and PIK-23)
http://www.tky.hut.fi/~pik/lekot/pik-koneet-frames.html
Jouni Laukkanen FI (GPL, MGPL) PPL(A) SEP, TOW