To be honest, for a solar charger in that range, a controller isn't really necessary, I don't think that you'll run any risk of overcharging the battery. Let me try calculate this just for fun:
Let's say your battery is roughly 40Ah, with a self discharge of 5% per month, or 2Ah per month, or .0666Ah per day. The vehicle will likely draw some power constantly, let's say the parasitic drain is 0.05A, or 1.2Ah per day, for a total of 1.2666Ah per day.
The solar charger, on the summer solstice in Pensylvania will receive 15h of sunlight, and assuming it's perfectly pointing at the sun the entire time with a 100% charge efficiency, the .27A charge current will recharge 4.05Ah of capacity. Arguably, you won't get anywhere near that power.
I've used the cheap-o $15-$20 5 watt chargers with no issue. I think the only thing to take note is that it has a built in blocking diode so that it doesn't discharge the battery when off, most of them do have it.