Mounting a box

I'm mounting a structural foam truck box. Can I bolt directly to the composite bed? If so what should I use to reinforce the attachment points underneath the bed (where the nuts will be) so the bolts don't break through the bed in a sudden stop or going over bumps? Bed seems kind of thin. Or should I bolt to metal?

 

I mounted mine to the bed and used 3/8"x1-1/4" washers.
It's about 300 lbs, loaded; no problems.
https://www.tacomaworld.com/threads/truck-bed-tool-boxes-thread.449662/#post-13169830

Edit to add;
Use a unibit to finish for cleaner holes.