i think i read somewhere someone made calculations on the ratte armor
considering the weight (1000 tonnes) ,measurements of the thing, + weapons that were supposed to be used the armor would have just been like 50mm all around. sure you could cut armor on buttom and add it somewhere else but in total it would have been very weakly armored.
so to get some real armor on that thing you would have to increase the weight alot, almost doubling it to get a real good armor. meaning that thing would be even slower and gooble down even more rescources to produce and even drive.
and yes 1 simple fighter bomber would have been able to blow that thing up if he scores a nice hit.