I ended up ordering a Victron Energy Multiplus inverter from Amazon. The Magnum MSH4024M would have taken longer to ship and it can't be used with the terminals on the bottom without a conduit box. there are some pretty cool new RV inverters from Xantrex and Magnum, but only 12 volt.
My backup plan if the Victron is late is to try to fix my Prosine by swapping in the relay from the broken Prosine 3000 I have. I have no idea what actually broke in the broken Prosine I have.