60w of goodness and I'm in Miami, so I get a lot of solar hours down here and I agree that most people assume too many S.H. when they're thinking things through. Unless you want to babysit your rig and I'm in a condo, bigger will be better because it will be faster, IMO. Together, those two 30w with hardware weigh in at ~2kg/11#, but moving up to the 40w panels, things start adding up, when dealing with rigids.
You can find the milspec, foldable 62w PowerFilms, but they're over $800 the last time I checked this past August. Rigids are heavier, but more durable, have longer warranties and those pictured above are mono-crystaline, so a bit more efficient than the polys and CIG/Thin Films portables.
Also, as semiman mentions, you have controller and charger inefficiencies, so you can never assume 100%. I don't think that my Morningstar SS-10L has a 30% loss, but I can see the controller and any of my battery chargers getting close to that number. Figure on 75% useful output when calculating this stuff and you should be close to reality.
Doing a SLA/AGM, you only have to deal with say...half of that number, becuase that Morningstar SS-10L IS a battery charger, but there's still going to be less than the full pie going in.
Also, the smaller controllers have certain limits to how big a battery they can charge and I don't think that they're meant to charge up a totally dead car-type battery, if I remember the manual correctly, so keep that thought in mind when putting something together.
Anyhow, it was a fun project to do and I think something like my rig, or a nice size foldable panel, are necessities where I live and I'll be waiting during this hurricane season, but I'll be ready!
Chris