Solar trickle charger

Going into my first winter with my camper, I've been studying how my coach battery charges. I've been checking the voltage at the battery and then monitoring how it responds to running the generator and driving the coach/charging off the alternator. It seems to take a LOT of generator time to charge up the battery (say from 70-80% discharged). I'm also planning a trip in April that will involve 7 consecutive days/nights of boondocking in a hotel parking lot (access to bathroom/showers, but no electric). I've been thinking about getting a solar panel to help with the situation. Here's one I'm considering:

http://www.amazon.com/Lowest-Price-THE-YEAR-Regulating/dp/B0046DSLFS/ref=sr_1_4?s=automotive&ie=UTF8&qid=1419200608&sr=1-4&keywords=solar+battery+tender+100w

Opinions/advice?