It's easy to use the Lightroom Plugin to upload to SmugMug!

 Use the Library and Develop modules, get your photo just the way you want it.  Then, right click on the photo or use the file>export menu, and click "Export..."

Then, you will see the Lightroom Plugin Menu.  Make your choices as below, modifying as needed.  IMPORTANT:  Use sRGB, and be sure to NOT check 'minimize embedded metadata.' 

You can choose an existing gallery or make a new one.