Maybe you could build a secure platform to help hold the ladder in place and sturdy. Keep the ladder firmly on the ground, but clamp or otherwise attach it to a frame that stands several feet high. I'm visualizing one made of 2x4s, with a 4' x 8' base (or what room you have) to give lots of stability, with a second frame 4' up from that, connected with lots of 2x4s for more stability, and all staked into the ground. You don't need a platform on top, just some crosspieces to attach to the ladder. You could also build a small box to keep at the top of the ladder to hold your tools and supplies.