Outside storage for 3-5 years....

I like the fact that you're thinking 3 feet off the concrete. The absolute worst is gravel or dirt.

3-5 years? I'd seriously think about removing the fuel tank. Not much work and no worries about old fuel, moisture, rust etc.

I have no opinions on covers but I think I WOULD cover and take it off occasionally to air it out and monitor deterioration. A cover will help protect against interior deterioration and water leaks.

No offense but people in .CA, TX, and similar dry states probably don't realize what we are up against in "rusty" states.