I have not tried any WP plugin booking systems, but want to share some thoughts.
I look after one site which has travel related listings.
I use a custom booking system for accommodation.
The way I have set things up are like this:
Created a CPT for Accommodation
I do not allow users to add listings to that Accommodation CPT, but they can list in the booking system.
I then create an Accommodation listing using the URL of the booking page.
Because the Accommodation CPT listings are only editable by me.
All other listings in other CPTs are normal GD listings which can be submitted by users.
All listings including the Accommodation are on GD maps and GD searchable.
I hope I made sense: a simple solution without any need for customisation.