A few years ago I rode a mountain bike on the White Rim Trail in Canyonlands NP. 80 miles of bumpy. I carried my EOS3, a couple of lenses (28-70L, 100-400L) and strapped the tripod on the back of a Lowepro Nature Trekker. The hip belt is a must. No problems.
One suggestion. I had a 10 mile trail near my place at the time. Before the trip to Canyonlands, I rode that trail packed just like I was going to be for the trip. Then I made it a point to photograph all kinds of things along the trail to get used to removing the pack, setting up, packing up, and riding just a short distance (sometimes just a 100 feet) to the next shot. This helped train myself to realize that it isn't as big a pain in the rear as it seems and I worked out any packing/procedural issues so I wouldn't be surprised in the middle of nowhere.
So whatever your choice (sounds like you are leaning to a bike mounted system) do some test rides, get used to the fact that the camera isn't as readily available. Make it so that, in your head, getting the camera is not a huge production, it is merely part of the process and shouldn't frustrate you to where you will ride right past a shot because you don't feel like hauling out the gear.
This shot entailed straddling the tripod over the bike