Hi!
Ofcourse inside is best!
I have flown pylonracers, seaplanes , twins , scale ,sailplanes, aircombat...you name it ...all with flying wires inside ...and have had no problem whats so ever with interference ...last time I placed the antenna outside ...up to the fin was 30 years ago when I had only flown a year and was a newbie.

Regards!
Jan K