Huge water volume loss during boil

Hi all,

I've brewed 3 batches now, all stovetop since my propane burner (Bayou Classic) doesn't really have a good raised stand to burn on, which would make my gravity spout useful for transferring to my primary. I always start with 6 gallons of water to account for loss due to steaming, but I always end up with 3.5-4 gallons total at the end -- that is a freaking lot of steam loss.

Should I cover my pot when I'm raising the temp to boil, and then remove when nearing boil to avoid boilover? As it stands, it takes about an hour to get to 170º so I can remove my steeping grains, and then about another 90 minutes to get to boiling, turn off the heat, add the malt, and then by now it's already down to 195º so it's another 30 minutes or so to get back to boiling again.

Any suggestions while I try to figure out a cheap, heat-resistant, sturdy structure?

P.S. I forgot my main question -- I considered topping off with water, but my OG readings are always exactly to the recipe's specifications, so I feel like I'd be watering my brew down. If I'm hitting the OG perfectly, how am I ending up with fewer than 4 gallons of beer for what is a 5 gallon recipe?

You'll have to wait for the experts for most of your answers, but 2 and a half hours to get to a boil? Did I get that right? An hour to 170, and 90 MORE minutes to boil?

I wonder if you've got a burner problem. I use a Bayou Classic and I'm boiling in way under an hour.