Fuses are a really good idea. Seems like my maxifuse holders aren't as big as Ryans, but they do take space. Not sure which I'll use here yet. I have some others:
You can bolt onto these fuses with flexible wire, and then heatshrink over them. Mouser or Digikey had them, they are electric vehicle fuses. Not cheap but not terribly expensive. They are bigger than maxifuses but not needing a holder helps some. I also think that bolting to a maxifuse might be a better way to use them. More on that theme to follow.
How about this:
Drill a #10 hole in each lug of a maxifuse. Use two wires and two ring lugs bolted to each maxifuse lug. One ring lug on each side to get maximum surface contact area. Then join the two wires into the bullet, so the two wires are in parallel. Use two #10's or #12's on each side of the maxifuse. Use a brass #10 screw or bolt to bolt them together to improve the conductivity, though most current will go wire to ring lug to fuse lug anyway. I suspect that would be adequate for 50 amps, but try it and then check to see if the connections get hot. If they stay warm or cooler then it passes!
I have also used fusible link wire on systems like these. Make up a short fusible link section with ring lugs on the ends, or perhaps bullets or whatever connector fits your setup. Maybe put some clear silicon high temperature tubing over the fusible wire in case it melts to try to keep it from the batteries and other vulnerable bits.