So assuming I can only push 30W per channel, would these speakers sound alright.. and I don't mean would they work, I mean would 30W be sufficient to drive these decently.

Your ears may not be able to detect it, but if the amplifier is only capable of 30W RMS, and the speaker's minimum RMS is 50W, then there will be distortion. You need to be sure of the voltage that is being supplied to the amplifier. You can put a meter on your battery to find out what its actual output voltage is.

But in my amateur opinion, even if that amplifier was receiving 14.4 volts, and its output was at the higher specs, I still wouldn't use those speakers with that amp. I'd want the amplifier's RMS rating to be somewhere inside the RMS range of my speakers, not right on the edge. For example, my current 6.5" speakers have an RMS range of 2-50W, and my current CD receiver's RMS ability is 22W. If I decide one day to finally get an external amplifier that was more powerful, I would get new speakers as well, so that my amp's rating fell somewhere near the middle of my speaker's RMS range.

Edit:
BTW, peak power on the amp is 90Wx4 if that helps.

I wouldn't use that rating as a reference point when selecting your speakers. At peak power, you would very likely have distortion (clipping).