Sorry for not getting back sooner.
I am a little confused by morningstar's product, and what it can handle as it says it is for 12 or 24 volt systems. I am not sure if a 24 volt panel would release the magic smoke, or if the controller would only output ~50% of the panel's juice. I would think for a 24 volt system it could handle a 24 volt panel, but whether it could step down the voltage and double the amperage as a MPPT type controller does is unlikely.
But it is best to be sure.
Generally 24 volt panels need a MPPT type controller and those are significantly more expensive than a PWM.
With a 10 amp charge controller I think you should look for a 12 volt nominal panel in the 180 watt or under range. But most panels over 140 watts are 24 volt nominal panels.
The open circuit voltages will be around 20 volts. The voltage at max power will be around 17.5.
If the 20 amper is not too much more and With Amazon's easy return policy, You might want to get the bigger controller just in case you find that your solar is short of your needs and you want to add another portable panel. But you can also just get another 10 amp controller and run them in parallel if more becomes necessary.
To take max advantage of the panels energy, you want to use pretty thick wire between panel and controller. At least 10 awg, and even 8 awg if you have 25 feet between controller and panel, one way.http://genuinedealz.com/
Pretty good prices, free and fast shipping.
Also for ease of connecting and disconnecting the panel to the charge controller:http://www.andersonpower.com/products/standard-powerpole.html
You do not want to bust out the screwdriver every time to connect the panel to controller.