is there a way to effectively train for Trail marathons and ultras and still compete well in Cyclocross? I've been running since i was in Middle School and I started riding roads about 2.5 years ago and now want to get into Cyclocross while also preparing for my trail races. I'm by no means really hardcore about cycling (only about 150-180 mpw with 50 mpw running) so really intense suggestion may not be necessary.

note: the reason i picked up the cycling was b/c my body really cant take much of the pounding of running (even on trails) without an impact related injury.