interesting, i wouldn't think a couple LEDs would drop the system that low seeing as they don't draw much power, but I didn't realize that. Seems like wiring them in series would be the logical way to do it, I think it would work just fine but I've never tried it.
OP those side markers look alright, but keep in mind a lot of those cars that come with them actually have an indent in the fender for them to mount. You're going to want to make sure the ones you get are made to mount on a flat surface, otherwise it's going to look and fit pretty horrible.