The floor inside all my microwaves, under the glass tray, rusts out.

rust dissolvent only on the rusted part (wheels?), then use appliance epoxy to respray the area where the paint is peeling after using a fine sandpaper on it. Condensation after cooking needs to be wiped out or door left open a min. to release . Often check the holes atop the compartment to see they aren't blocked w/food spatter.

To be safe, get a new microwave. The prices of microwaves has come down tremendous...much less than the cost to repair a home if the thing catches fire!

Caution: Appliance epoxy spray paint is made to fix cosmetic issues on the OUTside of appliances!!!!! The high heat in a microwave can cause the paint to release fumes which would obviously be toxic! You wouldn't want to breath those fumes, and you definitely wouldn't want your food inside the microwave to absorb the fumes. The food would smell awful, and it would not be safe to eat. It may be helpful to realize that not everything that breaks should be fixed. It seems that some of these inexpensive microwaves and other small kitchen appliances are what I call 'disposable'. Things are not intended to last forever, and some things broken should be thrown away. Especially things we use for food prep. I'm jus sayin...

replace the unit; and after you use it for anything, keep the door open a few moments to reduce the steam that accumulates; keep that little track under the plate dry -- it will collect moisture from your heating things ( not 'spills' ); just wipe with a paper towel every time you use the unit for anything -- it will keep it DRY, and clean at the same time -

How old is it? what so you clean it with?