I did something similar last July. Here's a shot of my set up. I have a Bushnell Spotting Scope - Discoverer Zoom Telescope. It is 60X and it included a F mount - bonus. I attached it to my D70. According to the adapter, it can provide an equivalent 4000mm lens.(!) My tripod carrier was slung from the tripod and had a ten pound lifting weight in it for stability - I had to. And, I was able to achieve a good shot or two. I hope you will keep trying - I will.
"The Nikon did the work; I just happened to be behind it at the time." TP