Is it permissible to continue missing Friday prayer due to frequent work-related travel? And are there any restrictions on that?

There is no blame upon the traveler if Friday prayer overtakes him and he is unable to perform it. However, if he is able to attend it without hardship – such as being close to the mosque – then it is not permissible for him to abandon it, and he must repent if he abandons it while being able to perform it.