How to make sure steering box doesn't loosen up?

The hardened 1/2" X 13 TPI fasteners bolting my steering box to the frame have loosened. What's the best way to make sure they don't loosen again? Should I use Loctite red or blue? Red is stronger, but might require heat if I ever want to remove the box some day. Is blue strong enough? Since I'm using thread lock, do I need to put a lock washer under each fastener, or should I just use a hardened plain washer?