Best tool for those hard to reach bolts is a swivel head ratcheting wrench. Complete set may be close to the same price as a single 13mm. Harbor Freight versions maybe? Spray them with penetrant first, the drain holes are directly above them. Thank Eddie S for the tip on the Gearwrench.
To add, after dropping the spare tire, unbolt the EVAP canister and move it for added clearance. Also wouldn't hurt to lightly coat the bolt threads with anti seize for future ease of removal.