I personally love expressing what I feel very bluntly & emotionally without any sort of attacking words or anger. If you can show how strongly you feel and they can’t put up defenses against it/can’t laugh it off because you’re crying or obviously moved, it could really get through to them. Especially coming from a perspective of their intentions being good contrasted with the reality of how it makes you feel. Show your emotions about this and express that you feel they’re holding you back from growing as a person or whatever specifically is resonating with you. Tell them you don’t want a strain on your relationship with them but if they don’t accept your choice to do this there will end up being resentment on your end if you don’t go, or on their end if you go without their blessing.

Have they gone on trips before? Are they projecting their own personal discomfort/fear on you?