I have a rt142.
I made up a couple of long bits of board to go on the bottom bits of the door to help extend the depth so the speaker magnet wouldn't hit or touch the door metal, covered them in carpet to match the doors. Stuck in some nice titanium 4 1/2 inch pioneer 3 ways.
Threw a 12 inch sub in the boot, mounted a 80w RMS x 4 amp on a another board in the side opposite to where the jack and tools are kept. Loud as fuck.
Didn't put speakers in the parcel shelf, not enough room, if you put in another board to give it some height it should work, theres a couple of spots to stick the end magnet out.
I think the original speakers are 4" so you could probably just replace them with new ones.