Gmap Views Module - Popups are too big
looking at the details from https://stackoverflow.com/questions/5186047/drupal-gmap-views-popups-are-too-big I would suggest to wrap everything in the custom text field in a div with a specific class then do .myclass { width: DESIRED_WIDTH; } in your stylesheet.

or try to div.gmnoprint .views-field-nothing { width: DESIRED_WIDTH; } where div.gmnoprint is the wrapper div for the gmap popup and .views-field-nothing is the default wrapper for a custom text field in views.

Without a live example, it is harder to give an exact answer. I suspect you may have to add overflow:hidden; to your wrapper div if you have any floating going on there.