you have to take a closer look even at the routing on such a project. 100MBit requires extremly carefully routing (delay of the traces, capacitance, skew etc.) and i would not recommend OP's in such a project because there are some side effects that need a lot of debugging which is only effective if you are planning to do large series and want to spare some money there are some symmetrical digital transceivers from national which i would use. (hysteresis, delay etc.)
If you only wnat to extend a single line use a normal switch (not hub)! which might protect you from a lot of trouble! ;.)
Look any small Fast Ethernet switch chip (2 to 8 port), same of them
contains RAM and PHY, only most problem is Industrial temparature range ....
Redux AptaGate RS-120 have operating temparature from -40 to +85 C.
It need only add too PHY ( Intel LXT972A ) and SDRAM.