Awesome, thanks. It's in the eastern Oregon high desert, so lots of speed. I've never ridden this area, but I've ridden areas near by. I bought 3 of the Burton 1 liter fuel bottles that are supposed to work really well. I might pack 2, just because I don't think the weight will be a huge issue.
I have heard some people get as much as 45 miles out of the stock tank. If I could find a yellow desert tank, I would mount it up.
Once you are out riding you will not feel the extra fuel. Just pack it so it does not bounce around.
Back in the days of my racing, I had a stock tank on my 89 KX250 and was on a fast and technical 45 mile loop. I was carrying a quart of gas with me just in case I needed it. Well it just happens, I am battling a guy in my class with about 3 miles left to go and I as pull up along side him down this wide open wash, we make a hard left up out of the wash. I grab a gear and just as I am passing him, the bike bogs and runs out of gas. I used the gas I was carrying and made it to the finish without catching the guy. My buddy had the same year KX500 and bought a desert tank and I took his stock tank and mounted it on my 250. The stock tank on the 500s were 2.6 gallons and that is all I needed to do 50 mile loops.
Check out Clark gas tanks, they claim to make a 2.6 gallon tank in yellow. I am not a fan of Clark, but it might work for you.
Oh and you want weight? I was pre-running mexico for the Baja 1000 in 91 and had a 3.3 gallon tank on my 92 KX250 and had 2 1 gallon preston bottles full of gas, one on each hip to pre-run a 140 mile section. That was some great weight in the begining.
Sorry to get off topic...
