I was finally able to land on Duna with a full-function manned rover. That was...less easy than I thought. Turns out a simple transfer orbit is basically impossible unless you do a bunch of calculations and stuff...so the key was to escabe Kerbin’s gravity, establish a solar orbit kind of similar to Duna’s, match orbital inclinations exactly, then adjust the grow/shrink the orbit with prograde/retrograde burns until it almost exactly matches Duna’s orbit and wait for an encounter. Then you hope you have enough fuel to scrub off the speed, enter Duna’s atmosphere (use it to aerobrake), and parachute down to a gentle landing! Child’s play!
Then you realize your rover doesn’t have enough fuel/thrust to escape Duna’s significant gravity well, and that your Kerbal will die a cold, lonely death, millions of miles from his home.