They appear to make three variants, one glass fronted and the semi-flexibles, one of which is rated as a “Marine” version, the MSX-??MM where ?? = wattage. Here in the UK their distributorship includes Marlec Engineering Co Ltd. http://www.marlec.co.uk Who are about to quote me for a 30-watt panel, I’ll let you know how much, but it isn’t “cheap power”, as such!
Otherwise, there are the Non-Marine variants, much cheaper and lower output, such as the BZ51E quoted as giving out 12V at 500mA for £79.99 available from Maplins:- http://www.maplin.co.uk who are an electronic components retailer. Others here, have said these are good for keeping batteries topped up, no doubt they will chip in here with more info for you.
Mine, referred to by Colin, is a Solarex. It is now five years old and has begun to delaminate a little. I suspect that the output has reduced a little, but it seems to keep the batteries well up most of the time.