I am looking into these to replace an old propane heater for an inground pool. The heater burns about 3 gallons of propane per hour which is about $9 at current prices. Am looking for a good reliable DIY solar heater. I see there are many brands. Will be installing on the ground, on an angled support or flat on the ground. I think I will need 2 or 3 4x20 panels. Any suggestions as to brands? I see there are about 4 or 5 brands to choose from.