I just googled your problem, it seems like a common one. One fellow used the same clamps I have on my trailer.
Here is a better look at the clamps I got from carac trailer parts, you can adjust the hoop length (screws in/out) for the pressure you want.
Make sure you get sensor safe sealant, don't just use any old crap from bunnings.
Go to repco/autobarn etc and ask for sensor safe.
Let it cure really well before driving it.
You could use really big rivets, but they may not hold too well on the plastic box, so you could put a small aluminium plate inside, so they get a good grip.
Possibly bolts with lock nuts and washers may be easier.