[Mobile-Portable] 28-volt power?

[Randy]

Hi:
I am looking for a source of 28-30 VDC to power a mobile solid state
amplifier.  Somewhere there are probably 12 volt to 28 volt inverters but I
haven't been able to find anything reasonably priced or sized (I need
400-500 watts).

Of course there are lots of 120 vac inverters around and I was wondering
about using one of those to power a 28-volt switching power supply.  I
realize many of those low-cost inverters do not produce very good sine waves
but would this be a big problem if used just for driving a switching power
supply?  Also, I can imagine all sorts of potential RFI problems with
something like this but I will deal with that if/when the time comes.

Anyway, any ideas?

de Randy, W7HR