For the front, consider a Tubus Swing. It mounts to the crown of a suspension fork, putting the load on the suspended part of the bike, and giving you much better ground clearance than most front lowrider racks.
The Tubus/Ortlieb combination is tried and tested. I've been using both for about a dozen years - a pair of Front Roller Lights front and rear on various bikes with different Tubus racks - and can't fault them.