45 watts won't give you much. Panel prices have really come down over the past few years. Check out AM Solar's web site. Tons of info and some great turnkey system options. They have a series of articles on the site that give you a good idea of what you need to meet your expectations. They also are very helpful over the phone.
If you're going to attach stuff to your A/S roof my humble advice is to get a system that will meet your needs and install once. I made the mistake of undersizing my last system and ended up with spending more $$ and more labor fixing it.
International Sterling 27FB
2015 GMC Denali 2500 Duramax & Allison