Devin, while it's probably fine to run AC and DC in the same conduit (AFAIK), you would want to make it obvious what's DC and what's AC. Not just obvious to you, but to anyone that works on your rig in the future.
Truth is, extension cord wire isn't rated to be enclosed in conduit... for either DC or AC service. It's meant for temprorary, exterior-type applications where the jacket is exposed to free air. Plus, the ground wire would make most folks think it's an AC circuit. THHN or similar would be applicable. CHeck you lamp cord, becasue it might not be, either.
Also check your voltage drops for whatever loads you're placing on them (remember to do a "round trip" calc. for DC). Here's a nice one online:
http://www.nooutage.com/vdrop.htmFor minor loads, 12AWG is sufficient. No sense going much below that, IMHO, because even moderate loads will suffer some voltage drop.
Wire is cheap in the grand scheme of converting. Fires and/or electrical woes... are not.
My $0.02,
Brian Brown