A little off topic but an option for mounting instead running bolts into the frame is you use a square u-bolt and open the hole on one end and slotting the other and you basically end up with a pair of studs hanging down, works great on thinner frames that easily strip out.
The "legs" would need to be shorter than pictured but you get the idea.
The "legs" would need to be shorter than pictured but you get the idea.