Planning/engineering for focused solar/battery system

[sanibel sailor]

I am engineering a small, very focused electrical system. I am planning a 300 mile adventure race in Florida in March aboard an engineless Windrider 16 trimaran. I'd like to be able to use my ST1000+ tillerpilot for say 6 hours a day. No other electric draws. Tight budget and no long term plans after this race.

Trying to figure out solar adequacy and battery size.

It says the unit pulls 0.5 to 1.5 amps, (0.04 on standby) but that is for a boat up to 6600lb. I hope that a very light boat will allow a short tiller arm, less motor excursion and consumption will be much reduced. I will need to adjust the gain way down.

1) Am I overly optimistic to hope for 3 amp hours a day usage?

I have a 20 watt rigid solar panel. It will be soft mounted and so I can adjust it to some extent to optimize output. Most likely limited to keeping it out of sail shade rather than perpendicular to the sun. At max output, around 1.5 amps. I will be using a cheapo eBay solar controller.

2) Is it reasonable to expect to get 3 or more amp-hours per day out of it in March in Florida?

Planning on getting a small Sealed Lead Acid battery, perhaps 18AH size, to run the tillerpilot. I will need to make or adapt a battery box as I don't think they are readily found in this size. Weight and volume are important. I don't want too big nor too small. As the battery is only $30 or so, I am willing to accept a short battery life associated with deeply discharging it, but it has to last the week or so planned trip. I will also have a separate small 3-5AH SLA battery charged to keep cell phone and handheld GPS going.

3) Does this seem like an appropriate battery capacity for this scenario?