Insecure Microwave

The microwave in our Bourton is loose.

I am aware that it’s held in place by four small screws which go into the body of the microwave from underneath.

The two rear  screws are loose in the body of the microwave allowing it to tip forwards. I have tried slightly thicker screws to no avail.

Before I put in  some really sizeable screws in has anyone else had this me come up with an alternative solution?

Remove microwave, remove glass turntable and wheels bit first.
Turn it upside down
Obtain rivnuts, google them, you'll need a setting tool as well. Drill existing holes carefully, don't let the drill go too far in, just open the hole.
Fit rivnuts
Replace microwave, screw down with proper machine screws correct dia for rivnuts, correct length too
Far better solution than the existing self tappers ( assuming that's what it had, my Warwick did)

I’ll have a look thanks

The way they fit the microwave is very unsatisfactory. I had to replace a Daewoo with a Russell Hobbs. I drilled through the existing shelf holes and took pot luck with which part of the base I hit. In the Broadway the space under the microwave is very tight for an electric drill and it was a fiddly job. I can’t see how you can drill the holes in the base of the microwave first because there is no way of locating them once the microwave is put into position. It all seems a bit random to me.
Ideally I would fix a couple of metal brackets , front to back of the microwave, using a strong metal adhesive then drill up from below into the bracket which would be a better target than some random points on the underside.

Right from from new our microwave seemed to rattle when on the road. I've jambed a short length of largish diameter silicone tubing between the top of the microwave and the surround, it prevents any movement working the screws loose. So far it's still working and I haven't needed the rivnut repair.