Thetford cover broken

Well, we made it through most of two seasons before cracking the cover of our Thetford Model 80 recirculating toilet. We had read where it is a weak link for the toilet and we were very careful to sit on the side of the cover when brushing our teeth, etc. but I must have forgotten a couple of weeks ago when it was colder than usual and it may have been brittle.
I plan to call Jimmie at the factory to order a new cover assembly, but, what has anyone done to strengthen their cover to avoid this problem happening again?
Dick_B

I just ordered a new one from Thedford at a cost of about $38.  I would also appreicate ideas as to how to reinforce it.