For bicycle touring, an underquilt is much less bulky than a foam pad. Seems to be no brainer - it's the best way to stay warm, especially around your shoulders as you lean on the hammock sides at night. Do it right. Get an underquilt, top quilt, get a quality cut tarp that can be set up in porch mode, or can be completely closed off during high winds or driving rain.

Here is my setup from last Saturday: