Like Kenny and David say; a plate on the opposite side of the bracket will reinforce any bolt hole you drill through the frame. In the case of a single hole, large diameter washers under the head and nut are best. If you're setting up a pattern of holes then a plate with the same pattern works as well. If you can afford one, or know someone who has one, a magnetic base drill is the only way to go for BIG holes. I did the baby HEMTT's cab and front skid plate mounts and the spring perch mounts with one set up for roto bits and it sure made life worth living again; especially for holes on the horizontal or up from the underside.
TIP: If backing up a bolt and nut with flat washers, use self-locking nuts. If you use lock washers, you're only locking the nut or bolt to the washer, not the frame. Lock washers are fine if you're using a backing plate with several holes as it won't spin on you like a washer will.